grim_d
Unlikeable idiot.
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- 4,218
- Location
- Scotland - Ayrshire
I contacted a bigg caliper refurbishment company recently to enquire about having some calipers done in the summer, I've recently had to put thread inserts in some of them.
They told me they do not do thread repairs of any kind nor will they refurbish a caliper that has had this kind of repair done, on safety grounds they consider them scrap, fair enough for a big company with insurance etc but it got me wondering, I've done some low grade testing today with my spare inserts, I was particularly curious about the strength of them in a standard installation, as in drilled and tapped by hand, we all know a hole drilled by hand always ends up a shade bigger but I wanted to go extreme.
Brand of the kit is v-coil by Volkel and the size is M12 X 1.5 with 1.5d inserts.
The bolts are the old ones from the calipers, they have 11 stamped on them so grade is unknown but possibly 10.9 but at least 8.8 I would assume.
I used a peice of 20mm thick extruded aluminium scrap so the Insert could go full depth. I know it isn't terribly scientific with different grades of aluminium used but it's interesting none the less.
I did 4 in total and tightened a bolt with a 1/2 inch ratchet until I couldn't anymore and then moved to a breaker bar until failure..
The drill for the inserts is 12.4mm and the OD of the tap/inserts is 13.9mm, that gives the inserts 1.5mm of engagement. (0.75mm per side)
Hole 1
A control? Thread tapped in aluminium, no Insert, I was able to strip the threads in the aluminium but I had to use the breaker bar.
Hole 2
Standard installation of insert by hand. I was able to shear the bolt using the breaker bar, I was able to remove the stud easily and thread a new bolt in and tighten it fully with the ratchet.
There was some possible minor deformation of the first few threads as I could no longer easily spin the bolt in with my fingers but it went in easily with the ratchet and I could tighten it as much as my arms would allow
Hole 3
Installation of insert as normal except I jiggled the drill about and made a bit of a mess of the hole. The top of the hole ended up at 13.1mm
I was able to tighten it as above but I did not take it to failure as I had limited bolts and wanted to go further, I have no doubt the bolt would have sheared.
The very end of the coil had moved slightly because it basically had nothing to grip but popped back down and I could thread a bolt in again.
Hole 4
This time I drilled a hole that was approximately 13.1mm, so only 0.4mm of thread engagement per side.
It should be noted that the Insert felt noticeably loose during Installation but held fine when putting the bolt in.
Sheared the bolt, again possible minor deformation but otherwise fine as per hole 2.
Hole 5
This time I moved up to 13.5mm hole, only a tiny 0.2mm engagement per side.
At this point the aluminium failed and pulled the insert out, I was able to do this with ratchet.
So my conclusion here is that (unsurprisingly) helical coil inserts do indeed make threaded holes in aluminium far stronger even if the hole has been drilled a bit cack handedly. Being able to shear a high tensile bolt even when engagement of the insert is almost 50% less than is should be is quite impressive to me.
That being said, I would always recommend your holes to be within manufacturers specifications!
Hope this was of interest.
They told me they do not do thread repairs of any kind nor will they refurbish a caliper that has had this kind of repair done, on safety grounds they consider them scrap, fair enough for a big company with insurance etc but it got me wondering, I've done some low grade testing today with my spare inserts, I was particularly curious about the strength of them in a standard installation, as in drilled and tapped by hand, we all know a hole drilled by hand always ends up a shade bigger but I wanted to go extreme.
Brand of the kit is v-coil by Volkel and the size is M12 X 1.5 with 1.5d inserts.
The bolts are the old ones from the calipers, they have 11 stamped on them so grade is unknown but possibly 10.9 but at least 8.8 I would assume.
I used a peice of 20mm thick extruded aluminium scrap so the Insert could go full depth. I know it isn't terribly scientific with different grades of aluminium used but it's interesting none the less.
I did 4 in total and tightened a bolt with a 1/2 inch ratchet until I couldn't anymore and then moved to a breaker bar until failure..
The drill for the inserts is 12.4mm and the OD of the tap/inserts is 13.9mm, that gives the inserts 1.5mm of engagement. (0.75mm per side)
Hole 1
A control? Thread tapped in aluminium, no Insert, I was able to strip the threads in the aluminium but I had to use the breaker bar.
Hole 2
Standard installation of insert by hand. I was able to shear the bolt using the breaker bar, I was able to remove the stud easily and thread a new bolt in and tighten it fully with the ratchet.
There was some possible minor deformation of the first few threads as I could no longer easily spin the bolt in with my fingers but it went in easily with the ratchet and I could tighten it as much as my arms would allow
Hole 3
Installation of insert as normal except I jiggled the drill about and made a bit of a mess of the hole. The top of the hole ended up at 13.1mm
I was able to tighten it as above but I did not take it to failure as I had limited bolts and wanted to go further, I have no doubt the bolt would have sheared.
The very end of the coil had moved slightly because it basically had nothing to grip but popped back down and I could thread a bolt in again.
Hole 4
This time I drilled a hole that was approximately 13.1mm, so only 0.4mm of thread engagement per side.
It should be noted that the Insert felt noticeably loose during Installation but held fine when putting the bolt in.
Sheared the bolt, again possible minor deformation but otherwise fine as per hole 2.
Hole 5
This time I moved up to 13.5mm hole, only a tiny 0.2mm engagement per side.
At this point the aluminium failed and pulled the insert out, I was able to do this with ratchet.
So my conclusion here is that (unsurprisingly) helical coil inserts do indeed make threaded holes in aluminium far stronger even if the hole has been drilled a bit cack handedly. Being able to shear a high tensile bolt even when engagement of the insert is almost 50% less than is should be is quite impressive to me.
That being said, I would always recommend your holes to be within manufacturers specifications!
Hope this was of interest.