Slow Monster rebuild - Page 52

350TSS · 16-10-2018, 06:34 PM

Sitting here with a small headache having been fibre-glassing the patterns today, I wanted to keep the temperature up so the resin cured nicely which meant the door of the shed closed and therefore an excess of acetone fumes. Good progress though as all the “easy” patterns were given a coupling resin coat on the back of the gel coat which was nicely tacky from yesterday and at least one layer of 100g chopped strand mat. Tomorrow they will get 3 layers of 300g chopped strand mat and if the release agent works as it should the following day I will have some moulds.

post pics

350TSS · 16-10-2018, 06:38 PM

In between coats I thought I would see if I could resolve my brake hanger clearance issue. The more I thought about it and drew it out I could not understand why the disc was not sitting central to the calliper. I was really sure that I had measured it right and made it so that there should not be a problem.
It turns out the problem was a mismeasurement on my part not on the lateral positioning of the disc but rather on the distance of the calliper from the centre of the wheel spindle. I had made my brake hanger and drilled the mounting holes for the calliper 0.5mm too small a radius. This was compounded by the cheapo Chinese disc which had a radiussed outer edge. The edge of the Brembo disc is right angular. So the new disc was c 0.25mm larger than OEM although the machined (wearing) face was the same size.
The bridge of the calliper was fouling the outer edge of the disc and would not permit the hanger when the spindle was inserted to sit square. The spacering of the disc outwards was correct but the calliper could not straddle the disc at right angles.
I had 3 options at this point
1. remake the hanger bracket – I really could not face a Mk 5
2. relieve the inside of the bridge of the calliper by 0.5mm – not easy to do and I do not want any swarf or filings anywhere near the seals (which are OK)
3. reduce the OD of the disc – I checked the pads run inside the OD so no loss of braking swept area and no risk of the pads getting a wear lip on the outer edge.
I came up with this contraption

which put it in the pillar drill and applied a 115mm angle grinder with a floppy abrasive wheel in and the disc is now 1mm smaller on OD (and about 20g lighter).
Lo and behold the brake hanger now fits – result.

upload png

350TSS · 16-10-2018, 06:41 PM

The clearance between the hanger and the disc attachment bolts will be resolved by machining 2mm off the head of the bolts, currently 5.6mm deep which will give we about 1.5mm clearance

350TSS · 17-10-2018, 05:00 PM

Bit of a slow day today, only managed one cladding of ¾ of the patterns with 300g chopped mat. It took simply ages to stipple it so that there were no air bubbles and I found that when I started on the second batch the first batch had developed air bubbles of their own accord, suspect it is due to the curing action generating a bit of heat or giving off some form of gas.

On the plus side:-
1) my estimated hours to completion dropped below 275 for the first time even taking into account an extra few day’s work obviously necessary to finish these patterns/moulds; and
2) these goodies arrived this afternoon, the wheel balancer, a jig for drilling nuts and bolts to enable them to be wired and titanium bolts for the callipers and discs and fork leg clamps. I think I have some incurable disease as I must be mad to spend more on this relatively meagre collection of bolts than I did on two new tyres

350TSS · 21-10-2018, 05:50 AM

The wheels now balanced, the balancer worked well. The front wheel required 20g and the rear 25g so I do not think I wasted my time. I did it without the discs fitted which might be a mistake.
It is one of those jobs though that it is very difficult to know when to stop. I made a mental rule that after adding a weight the wheel had to stop at 5 different positions (within any 10 minutes segment around an imaginary clock face if that makes sense) and then it could be considered in balance.
I had two slight concerns in the process: 1) I could only get 5g steel weights (which were not easily cut down as lead weights would have been) and I felt that I could have done a better job if I had access to 2g and 1g weights; and 2) The area where weights could be stuck to the Dymag wheel rim did not match the profile of the adhesive pad on the back of the weight (too narrow and slightly convex) so I have a concern that the weights may not stay where they were applied. I will take a couple of photos so if any go missing in the future I can replicate their replacement without removing the wheel.
Otherwise the mould making continues and all “easy” moulds have now had 3 layers of 300g chopped strand. I have used over 5kg of resin so far and these are all the smaller moulds.
I will leave the moulds for a couple of days to cure fully before trying to separate them. I am quite nervous of the outcome when I do try to split them as I have a lot of time (and not inconsequential money in materials, resin, hardener chopped strand glass mat) invested in getting thus far. Concerns are:
Will the mould separate cleanly from the pattern? And if not can I salvage the pattern for a second attempt?
Will the mould be an unblemished copy of the pattern or will there be air bubbles or cavities or other defects that require yet more work?

mickj · 21-10-2018, 08:05 AM

Try pre shaping the weights before fitting them, I still have some lead ones (I think they are lead) so it is easier.

350TSS · 22-10-2018, 03:02 AM

^^^^^ Trouble is the steel weights are about 3mm thick and not easy to bend to fit the rim. Any manipulation of them (bending them or cutting them with a hacksaw) means putting them in a vice and the (already marginal) self adhesive pad on the back does not survive this.

utopia · 22-10-2018, 09:45 AM

In the past, I've used pieces of lead flashing sheet and sticky rubber pads.
But proper weights are a more reliable proposition (and are available in 2.5g divisions).

Then again, the carbon wheels probably deserve some lightweight, titanium ones ......

Darkness · 22-10-2018, 10:48 AM

Quote:

Originally Posted by utopia

Then again, the carbon wheels probably deserve some lightweight, titanium ones ......

Special lightweight titanium wheel weights: now that would be bizarre!

350TSS · 23-10-2018, 03:52 AM

Whilst waiting for the moulds to cure completely I thought I would have a go at the calipers.
I have never really been a fan of Brembo gold brake calipers, it does not appear to be quite the same colour as the anodised disc carrier centre and is some way off the colour of the gold anodising on the forks and definitely doesn’t match Ohlins gold and is different again from the gold of the standard frame.
I will go for a tasteful satin black but I am not sure whether to highlight the Brembo logo on the casting.
The rear caliper (my original M900 one) came apart relatively easily and cleaned up nicely. Oddly only one of the two bolts holding it together showed any sign of Loctite.
The front forks I am using are S4 (silver anodised, 25mm spindle and wider spacing caliper mounting bolts) so I had to buy second hand wider spacing calipers.
There are 4 x M8 x 40mm socket cap screws holding the caliper together. With the first front caliper I tried to split, it became obvious why these calipers were sold, two of the bolts were seized solid and the socket head on one bolt was mullered so badly even the next size torx bit was sloppy. I shall leave them overnight with penetrating oil doing its best, but I have the feeling that this will be an absolute sod to get apart. As someone once said “ as a motorcycle mechanic you are always only one broken (or seized) bolt away from a 3 day nightmare”. At that point I did not have the mental strength to look closely at the other front caliper.
My normal approach to this would be to resort to a 2lb lump hammer and / or an impact driver but there is no way to support the back of the caliper casting such that the force of the blow is directed through the bolt only and I am worried about damaging /distorting the caliper alloy casting. A second option is to apply my brazing torch flame to the internal hex on the socket screw and hope the differential expansion rate of steel and aluminium breaks the Loctite, but I still have no means of applying a turning force to the bolt head.
I have little confidence that an “ease-it-out” will work as the shape of the casting is such that it will be very difficult to drill the bolt parallel and concentric to the bolt shank. Also the largest I could use would be about 4 to 5mm and I could end up with a worse problem of a broken hardened steel “ease-it-out” stub sticking out of a still stuck fast bolt.
My current thinking is to find the largest size imperial (1/4”) allen key that will go into the socket head and cut about a 40mm length, (the “sacrificial” allen key). I already have some ½” square drive allen key holders where the allen hex bit is retained by a grub screw.
I will then MIG weld the sacrificial allen key into the offending bolt (the heat should help with breaking the Loctite), remove the good allen key from my holder and fit my sacrificial allen key into my empty ½” square drive holder and thence to my electric rattle gun. The more I think about the more I am confident this will work – tomorrow will tell.

Darkness · 23-10-2018, 06:17 AM

Good luck!
There’s always Plan B though: sling it into a dark space under a bench and get another one.
I’ve a pair of used 65mm mount Brembo calipers somewhere which I bought ten years ago and haven’t used. Haven’t so much as looked at them in years though, so no idea of condition now.

Mr Gazza · 23-10-2018, 02:24 PM

The Allen key welding sounds favourite, but be careful with heat on the caliper in case you make a hot brake fluid gun! Best to have at least one piston out and preferably clean of old fluid, as it is very flammable stuff! More so than petrol.

I've got 4 calipers worth of these bolts to change. I seem to not be getting round to it!

350TSS · 24-10-2018, 10:53 AM

My ace plan did not work for two reasons, first, my ½” drive allen key holder would not fit the best fit allen key for the mullered socket head.
I decided to weld an allen key into the mullered head anyway.
The second reason was that the British made, finest steel allen key, during the welding process obviously imported some Italian cheese ions from the Brembo bolt because when I tried to undo the first bastard bolt it first bent then almost immediately sheared, leaving a perfectly welded 8 mm stub and a very secure, unmoved caliper casting connection bolt.
This left me in a bit of a quandary I could either drill it (say 3mm) out from the other side. I judged that I had two chances of drilling a 3mm hole in a high tensile(?) 40mm bolt concentric and parallel to the shank of the bolt i.e. - slim and none.
So I resorted to type and got the hammer out – Darkness’s Plan B was looming so I had nothing to lose anyway.
With the aid of a chisel, it worked on the three recalcitrant bolts out of the 8 bolts holding the two calipers together and the caliper castings, whilst suffering some bruising in the process, will be perfectly serviceable after a light dressing with a file and a couple of coats of satin black.
All this took a long time so nothing else got done today.
Sorry no pictures my computer of its own free will decided that it would no longer download pictures – no warning or alerts, no means of finding out why and worse no means of making it do what it is supposed to do - that is why I will always prefer carburettor bikes.

350TSS · 25-10-2018, 01:46 PM

For no apparent reason my downloading capability is back so here are the gory details

The cut throat razor in the last picture was bequeathed to me about 30 years ago and I have never used it (too frightened to shave with it) but finally found a use for it in trimming masking tape off the face of the caliper castings wher I do not want the paint to end up.

350TSS · 26-10-2018, 04:09 AM

Only grabbed a couple of hours in the garage today and I almost wish I hadn’t. Task was to modify 6 x 8mm x 30mm high tensile bolts to hold the rear disc to the rear wheel. I machined the bolt heads down by 2mm to clear the brake hanger and managed to get them very close to each other dimensionally.
I am not a huge fan of Loctite as I am never sure a) if I have the right grade; and b) if I have used too much or too little; and c) if re-using an old bolt whether I have got the thread free enough of oil/grease that the stuff will work.
Where dissimilar metals are involved I prefer copperslip grease and wiring as the means of stopping bolts undoing. Besides it looks nicer and it visually obvious that the bolt is secured.
I tried my drill jig for wiring bolts (see above), the drilling is designed to go through the angle of two flats of the hexagon head and the jig takes a 1.5mm drill. The first attempt resulted in a) a broken drill and b) a hole that had migrated so far towards the junction of the two flats that it broke through the angle i.e. not permitting any wire to be retained within the bolt head. Not a good start.
After the second attempt with the same result (only a fool makes the same mistake twice) I realised that a 1.5 mm drill is not stiff enough to attack high tensile steel at an angle of 60 degrees without bending and skidding down the slope. The drill jig does not and will not work, it might do if you were able to centre punch the spot to be drilled first but the chance of getting the centre punch hole to align with the spot where the drill emerges is quite small as there is no visibility when the bolt head is in the jig and no way of accurately knowing where on the in the depth of the bolt head the hole will be made.
The only alternative was to centre punch in the middle of one hexagon flat and drill right across the diameter of the head between two flats - 13mm of high tensile steel.
It appears that the outer 1mm of the hexagon is tougher than the core probably caused by the force used to form the bolt head. A new drill was sharp enough to cut through this outer harder layer and make its way 12mm across the bolt head, but by the time it got to the opposing harder layer it was blunt. Consequently it snagged and broke flush with the entry point. At this point I have machined 6 bolts and broken 3 x 1.5mm drills and not yet got an acceptable wiring hole in any bolt, worse I will have to machine 3 more bolts to replace the 2 with partial hole across the corner of two flats and one with a broken drill stuck fast within the head.
The technique now is to use a new drill for 12mm of the drilling and put a fresh drill in to accomplish the breakthrough. This drill can then be used for the next bolt for 12mm, an expensive way to carry on, one hole = 1 drill bit but it worked on the last 3 bolts
I budgeted 30 hours to drill and plate bolts as part of the build, this may need upward revision.

21-10-2018, 08:05 AM	#6
mickj Registered User Join Date: Jun 2018 Location: Clevedon Bike: M1200s Posts: 560	Try pre shaping the weights before fitting them, I still have some lead ones (I think they are lead) so it is easier. __________________ Keep the rubber side down. Mick

23-10-2018, 06:17 AM	#11
Darkness . Join Date: May 2007 Location: Stockbridge Bike: M900 Posts: 1,984	Good luck! There’s always Plan B though: sling it into a dark space under a bench and get another one. I’ve a pair of used 65mm mount Brembo calipers somewhere which I bought ten years ago and haven’t used. Haven’t so much as looked at them in years though, so no idea of condition now. __________________ Original and Best since 1993

23-10-2018, 02:24 PM	#12
Mr Gazza Lord of the Rings Join Date: May 2013 Location: Norwich Bike: M900sie Posts: 5,834	The Allen key welding sounds favourite, but be careful with heat on the caliper in case you make a hot brake fluid gun! Best to have at least one piston out and preferably clean of old fluid, as it is very flammable stuff! More so than petrol. I've got 4 calipers worth of these bolts to change. I seem to not be getting round to it! __________________

16-10-2018, 06:34 PM	#1
350TSS Too much time on my hands member Join Date: Jan 2013 Location: Shipbourne Bike: M900 Posts: 1,420	Sitting here with a small headache having been fibre-glassing the patterns today, I wanted to keep the temperature up so the resin cured nicely which meant the door of the shed closed and therefore an excess of acetone fumes. Good progress though as all the “easy” patterns were given a coupling resin coat on the back of the gel coat which was nicely tacky from yesterday and at least one layer of 100g chopped strand mat. Tomorrow they will get 3 layers of 300g chopped strand mat and if the release agent works as it should the following day I will have some moulds. post pics

16-10-2018, 06:38 PM	#2
350TSS Too much time on my hands member Join Date: Jan 2013 Location: Shipbourne Bike: M900 Posts: 1,420	In between coats I thought I would see if I could resolve my brake hanger clearance issue. The more I thought about it and drew it out I could not understand why the disc was not sitting central to the calliper. I was really sure that I had measured it right and made it so that there should not be a problem. It turns out the problem was a mismeasurement on my part not on the lateral positioning of the disc but rather on the distance of the calliper from the centre of the wheel spindle. I had made my brake hanger and drilled the mounting holes for the calliper 0.5mm too small a radius. This was compounded by the cheapo Chinese disc which had a radiussed outer edge. The edge of the Brembo disc is right angular. So the new disc was c 0.25mm larger than OEM although the machined (wearing) face was the same size. The bridge of the calliper was fouling the outer edge of the disc and would not permit the hanger when the spindle was inserted to sit square. The spacering of the disc outwards was correct but the calliper could not straddle the disc at right angles. I had 3 options at this point 1. remake the hanger bracket – I really could not face a Mk 5 2. relieve the inside of the bridge of the calliper by 0.5mm – not easy to do and I do not want any swarf or filings anywhere near the seals (which are OK) 3. reduce the OD of the disc – I checked the pads run inside the OD so no loss of braking swept area and no risk of the pads getting a wear lip on the outer edge. I came up with this contraption which put it in the pillar drill and applied a 115mm angle grinder with a floppy abrasive wheel in and the disc is now 1mm smaller on OD (and about 20g lighter). Lo and behold the brake hanger now fits – result. upload png

16-10-2018, 06:41 PM	#3
350TSS Too much time on my hands member Join Date: Jan 2013 Location: Shipbourne Bike: M900 Posts: 1,420	The clearance between the hanger and the disc attachment bolts will be resolved by machining 2mm off the head of the bolts, currently 5.6mm deep which will give we about 1.5mm clearance

17-10-2018, 05:00 PM	#4
350TSS Too much time on my hands member Join Date: Jan 2013 Location: Shipbourne Bike: M900 Posts: 1,420	Bit of a slow day today, only managed one cladding of ¾ of the patterns with 300g chopped mat. It took simply ages to stipple it so that there were no air bubbles and I found that when I started on the second batch the first batch had developed air bubbles of their own accord, suspect it is due to the curing action generating a bit of heat or giving off some form of gas. On the plus side:- 1) my estimated hours to completion dropped below 275 for the first time even taking into account an extra few day’s work obviously necessary to finish these patterns/moulds; and 2) these goodies arrived this afternoon, the wheel balancer, a jig for drilling nuts and bolts to enable them to be wired and titanium bolts for the callipers and discs and fork leg clamps. I think I have some incurable disease as I must be mad to spend more on this relatively meagre collection of bolts than I did on two new tyres

21-10-2018, 05:50 AM	#5
350TSS Too much time on my hands member Join Date: Jan 2013 Location: Shipbourne Bike: M900 Posts: 1,420	The wheels now balanced, the balancer worked well. The front wheel required 20g and the rear 25g so I do not think I wasted my time. I did it without the discs fitted which might be a mistake. It is one of those jobs though that it is very difficult to know when to stop. I made a mental rule that after adding a weight the wheel had to stop at 5 different positions (within any 10 minutes segment around an imaginary clock face if that makes sense) and then it could be considered in balance. I had two slight concerns in the process: 1) I could only get 5g steel weights (which were not easily cut down as lead weights would have been) and I felt that I could have done a better job if I had access to 2g and 1g weights; and 2) The area where weights could be stuck to the Dymag wheel rim did not match the profile of the adhesive pad on the back of the weight (too narrow and slightly convex) so I have a concern that the weights may not stay where they were applied. I will take a couple of photos so if any go missing in the future I can replicate their replacement without removing the wheel. Otherwise the mould making continues and all “easy” moulds have now had 3 layers of 300g chopped strand. I have used over 5kg of resin so far and these are all the smaller moulds. I will leave the moulds for a couple of days to cure fully before trying to separate them. I am quite nervous of the outcome when I do try to split them as I have a lot of time (and not inconsequential money in materials, resin, hardener chopped strand glass mat) invested in getting thus far. Concerns are: Will the mould separate cleanly from the pattern? And if not can I salvage the pattern for a second attempt? Will the mould be an unblemished copy of the pattern or will there be air bubbles or cavities or other defects that require yet more work?

22-10-2018, 03:02 AM	#7
350TSS Too much time on my hands member Join Date: Jan 2013 Location: Shipbourne Bike: M900 Posts: 1,420	^^^^^ Trouble is the steel weights are about 3mm thick and not easy to bend to fit the rim. Any manipulation of them (bending them or cutting them with a hacksaw) means putting them in a vice and the (already marginal) self adhesive pad on the back does not survive this.

22-10-2018, 09:45 AM	#8
utopia No turn left unstoned Join Date: Jun 2010 Location: leicester Bike: M750 Posts: 4,545	In the past, I've used pieces of lead flashing sheet and sticky rubber pads. But proper weights are a more reliable proposition (and are available in 2.5g divisions). Then again, the carbon wheels probably deserve some lightweight, titanium ones ......

23-10-2018, 03:52 AM	#10
350TSS Too much time on my hands member Join Date: Jan 2013 Location: Shipbourne Bike: M900 Posts: 1,420	Whilst waiting for the moulds to cure completely I thought I would have a go at the calipers. I have never really been a fan of Brembo gold brake calipers, it does not appear to be quite the same colour as the anodised disc carrier centre and is some way off the colour of the gold anodising on the forks and definitely doesn’t match Ohlins gold and is different again from the gold of the standard frame. I will go for a tasteful satin black but I am not sure whether to highlight the Brembo logo on the casting. The rear caliper (my original M900 one) came apart relatively easily and cleaned up nicely. Oddly only one of the two bolts holding it together showed any sign of Loctite. The front forks I am using are S4 (silver anodised, 25mm spindle and wider spacing caliper mounting bolts) so I had to buy second hand wider spacing calipers. There are 4 x M8 x 40mm socket cap screws holding the caliper together. With the first front caliper I tried to split, it became obvious why these calipers were sold, two of the bolts were seized solid and the socket head on one bolt was mullered so badly even the next size torx bit was sloppy. I shall leave them overnight with penetrating oil doing its best, but I have the feeling that this will be an absolute sod to get apart. As someone once said “ as a motorcycle mechanic you are always only one broken (or seized) bolt away from a 3 day nightmare”. At that point I did not have the mental strength to look closely at the other front caliper. My normal approach to this would be to resort to a 2lb lump hammer and / or an impact driver but there is no way to support the back of the caliper casting such that the force of the blow is directed through the bolt only and I am worried about damaging /distorting the caliper alloy casting. A second option is to apply my brazing torch flame to the internal hex on the socket screw and hope the differential expansion rate of steel and aluminium breaks the Loctite, but I still have no means of applying a turning force to the bolt head. I have little confidence that an “ease-it-out” will work as the shape of the casting is such that it will be very difficult to drill the bolt parallel and concentric to the bolt shank. Also the largest I could use would be about 4 to 5mm and I could end up with a worse problem of a broken hardened steel “ease-it-out” stub sticking out of a still stuck fast bolt. My current thinking is to find the largest size imperial (1/4”) allen key that will go into the socket head and cut about a 40mm length, (the “sacrificial” allen key). I already have some ½” square drive allen key holders where the allen hex bit is retained by a grub screw. I will then MIG weld the sacrificial allen key into the offending bolt (the heat should help with breaking the Loctite), remove the good allen key from my holder and fit my sacrificial allen key into my empty ½” square drive holder and thence to my electric rattle gun. The more I think about the more I am confident this will work – tomorrow will tell.

24-10-2018, 10:53 AM	#13
350TSS Too much time on my hands member Join Date: Jan 2013 Location: Shipbourne Bike: M900 Posts: 1,420	My ace plan did not work for two reasons, first, my ½” drive allen key holder would not fit the best fit allen key for the mullered socket head. I decided to weld an allen key into the mullered head anyway. The second reason was that the British made, finest steel allen key, during the welding process obviously imported some Italian cheese ions from the Brembo bolt because when I tried to undo the first bastard bolt it first bent then almost immediately sheared, leaving a perfectly welded 8 mm stub and a very secure, unmoved caliper casting connection bolt. This left me in a bit of a quandary I could either drill it (say 3mm) out from the other side. I judged that I had two chances of drilling a 3mm hole in a high tensile(?) 40mm bolt concentric and parallel to the shank of the bolt i.e. - slim and none. So I resorted to type and got the hammer out – Darkness’s Plan B was looming so I had nothing to lose anyway. With the aid of a chisel, it worked on the three recalcitrant bolts out of the 8 bolts holding the two calipers together and the caliper castings, whilst suffering some bruising in the process, will be perfectly serviceable after a light dressing with a file and a couple of coats of satin black. All this took a long time so nothing else got done today. Sorry no pictures my computer of its own free will decided that it would no longer download pictures – no warning or alerts, no means of finding out why and worse no means of making it do what it is supposed to do - that is why I will always prefer carburettor bikes.

25-10-2018, 01:46 PM	#14
350TSS Too much time on my hands member Join Date: Jan 2013 Location: Shipbourne Bike: M900 Posts: 1,420	For no apparent reason my downloading capability is back so here are the gory details The cut throat razor in the last picture was bequeathed to me about 30 years ago and I have never used it (too frightened to shave with it) but finally found a use for it in trimming masking tape off the face of the caliper castings wher I do not want the paint to end up.

26-10-2018, 04:09 AM	#15
350TSS Too much time on my hands member Join Date: Jan 2013 Location: Shipbourne Bike: M900 Posts: 1,420	Only grabbed a couple of hours in the garage today and I almost wish I hadn’t. Task was to modify 6 x 8mm x 30mm high tensile bolts to hold the rear disc to the rear wheel. I machined the bolt heads down by 2mm to clear the brake hanger and managed to get them very close to each other dimensionally. I am not a huge fan of Loctite as I am never sure a) if I have the right grade; and b) if I have used too much or too little; and c) if re-using an old bolt whether I have got the thread free enough of oil/grease that the stuff will work. Where dissimilar metals are involved I prefer copperslip grease and wiring as the means of stopping bolts undoing. Besides it looks nicer and it visually obvious that the bolt is secured. I tried my drill jig for wiring bolts (see above), the drilling is designed to go through the angle of two flats of the hexagon head and the jig takes a 1.5mm drill. The first attempt resulted in a) a broken drill and b) a hole that had migrated so far towards the junction of the two flats that it broke through the angle i.e. not permitting any wire to be retained within the bolt head. Not a good start. After the second attempt with the same result (only a fool makes the same mistake twice) I realised that a 1.5 mm drill is not stiff enough to attack high tensile steel at an angle of 60 degrees without bending and skidding down the slope. The drill jig does not and will not work, it might do if you were able to centre punch the spot to be drilled first but the chance of getting the centre punch hole to align with the spot where the drill emerges is quite small as there is no visibility when the bolt head is in the jig and no way of accurately knowing where on the in the depth of the bolt head the hole will be made. The only alternative was to centre punch in the middle of one hexagon flat and drill right across the diameter of the head between two flats - 13mm of high tensile steel. It appears that the outer 1mm of the hexagon is tougher than the core probably caused by the force used to form the bolt head. A new drill was sharp enough to cut through this outer harder layer and make its way 12mm across the bolt head, but by the time it got to the opposing harder layer it was blunt. Consequently it snagged and broke flush with the entry point. At this point I have machined 6 bolts and broken 3 x 1.5mm drills and not yet got an acceptable wiring hole in any bolt, worse I will have to machine 3 more bolts to replace the 2 with partial hole across the corner of two flats and one with a broken drill stuck fast within the head. The technique now is to use a new drill for 12mm of the drilling and put a fresh drill in to accomplish the breakthrough. This drill can then be used for the next bolt for 12mm, an expensive way to carry on, one hole = 1 drill bit but it worked on the last 3 bolts I budgeted 30 hours to drill and plate bolts as part of the build, this may need upward revision.