Drilling Torque Limiter?

[miken]

Hi, wondering if the MarkVII has any type of drilling friction torque limiter? I was drilling some aluminum and seized the bit in the stock. The motor kept running but the drill chuck and bit was not turning. I stopped the motor, loosened the bit from the chuck and reversed the bit with some pliers. I retightened the bit and turned it back on an all was fine, chuck and bit turning again. My question is did I damage something?

I found a similar thread here: viewtopic.php?f=10&t=21357&p=248364&hil ... ue#p248364 but I don't think my quill was extended very far.

Thanks, Mike -

[nuhobby]

I recently posted a thread about "PowerPro helping the Man" where I drilled a bunch of aluminum castings at my home shop, for the workplace's benefit. Small holes in aluminum (up to 3/8") were no problem for the Shopsmith in drill-press mode. However, the large 1/2" diameter holes would frequently have a seized bit. I ended up using the PowerPro to start the 1/2" holes in accurate locations on the drill-press, then I would take the aluminum parts to a different wood-vise to finish the holes with a 1/2" bit in a hand-drill. The hand-drill would have the advantage of wobbling around a little, which helped the bit to "jump past" the points where the bit wanted to seize.

[RFGuy]

I don't have a Mark VII, but from what I understand it has the same variable transmission (sheaves) that the Mark V has. So, if a drill bit, sawblade, etc. gets stuck in the material then it is possible that the belt will slip in the sheaves preventing damage to the motor. You should recognize it fairly easily though. Probably will have a burnt rubber smell and/or smoke from the belt slipping. Might want to check the belt and see if it needs replacing and/or tightening.

[miken]

I recently posted a thread about "PowerPro helping the Man" where I drilled a bunch of aluminum castings at my home shop, for the workplace's benefit. Small holes in aluminum (up to 3/8") were no problem for the Shopsmith in drill-press mode. However, the large 1/2" diameter holes would frequently have a seized bit. I ended up using the PowerPro to start the 1/2" holes in accurate locations on the drill-press, then I would take the aluminum parts to a different wood-vise to finish the holes with a 1/2" bit in a hand-drill. The hand-drill would have the advantage of wobbling around a little, which helped the bit to "jump past" the points where the bit wanted to seize.

These were just two 1/4" holes, I did use oil. The bit was likely dull, but seemed to cut ok up until it stopped. Both times it seized was when it was coming through the opposite side.
Thanks, Mike -

[miken]

I don't have a Mark VII, but from what I understand it has the same variable transmission (sheaves) that the Mark V has. So, if a drill bit, sawblade, etc. gets stuck in the material then it is possible that the belt will slip in the sheaves preventing damage to the motor. You should recognize it fairly easily though. Probably will have a burnt rubber smell and/or smoke from the belt slipping. Might want to check the belt and see if it needs replacing and/or tightening.

I stopped the motor almost instantly, maybe 1 or two seconds. I didn't smell any burning. I guess that is my second question; are the sheaves designed to provide slip at a specific torque load, or is the plastic coupler in the quill stripped or slipping somehow?

I need to pull the quill to add more tension to the return spring anyway, so I will see if I can notice any damage.

Thanks, Mike -

[reible]

What most likely happened was that the belt slipped. I've run into this most often with large Forester bits at low speed but anytime thing stop or start to stop it is either the motor or belts slipping, and as you indicated the motor was still going so....

The belt likely to slip is the the flat grooved belt and there is an adjustment to make that tighter which might be necessary.

BTW you can modify twist drill bits by putting a very small flat at the cutting edge, this makes it less aggressive, I learned this when I was working in a machine shop many many years ago.

Ed

[miken]

What most likely happened was that the belt slipped. I've run into this most often with large Forester bits at low speed but anytime thing stop or start to stop it is either the motor or belts slipping, and as you indicated the motor was still going so....

The belt likely to slip is the the flat grooved belt and there is an adjustment to make that tighter which might be necessary.

BTW you can modify twist drill bits by putting a very small flat at the cutting edge, this makes it less aggressive, I learned this when I was working in a machine shop many many years ago.

Ed

Good info. I don't mind much if it is just the belt slipping at high torque. I think these are the original belts anyway and I think that grooved belt is stretched as my eccentric is rotated pretty far. That makes sense. I will try that drill bit modification. All my bits are bad anyway, I doubt I could hurt it much. Been thinking of getting one of those drill doctor grinders.

[chapmanruss]

Mike,

This has already been said but I'll throw in a little history. From it's introduction changes to the Mark 5 were mostly in the Headstock itself. Two problems quickly showed up. One was solved by adding a clutch to the Drive Sleeve to help prevent breaking the Gilmer Belt. The other is unrelated to this. Later the drive system was changed to the Poly V Drive and the belt itself acted as a clutch to prevent damage to the drive parts. When something jams the drive system slips by design.

It seems that when drilling metal that last little cutting done as the drill bit comes through the other side of the material is when it is most prone to "catching" the drill bit. I have experienced it too.

[rpd]

What Russ said.

If you are drilling through thin metal, try using step bits, They give nice clean holes, and are less prone to catching.
Link to examples, They are available pretty much anyplace that sells tools.


https://www.harborfreight.com/search?q=step%20bit
.

[miken]

Later the drive system was changed to the Poly V Drive and the belt itself acted as a clutch to prevent damage to the drive parts. When something jams the drive system slips by design.

Glad to hear this. I did pull the quill and everything looked normal.
Thanks, Mike