Clamp and fixture projects

[Dabbler]

with just 3 points of contact

I would have mentioned the 3 point thing, but in aluminum to mill steel - I was worried it would be a little weak.

 

[PeterT]

Good idea Dabbler. That solves the 'how to clamp a smaller diameter with a larger hole'. But I don't think it solves what I was referring to - clamping multiple pins of varying random diameter. This drawing is exaggerated to show what I mean. Green pin is smaller OD than pink pin. Now if tolerances don't vary much, the difference may get taken up in jaw distortion. But if they are perfectly rigid bodies & the front & rear of jigs are constrained by parallel main vise jaws closing, then the small pin wont get the same squeeze. Or, assuming the small pin is clamped on the tangent, then the big pin will not fit the hole the same way.

 

[Dabbler]

@PeterT You are right! 100%...

This is where the 3 point contact thing comes in handy.

If Janger has centreless ground stock (like 01 drill rod) then they are close enough to clamp with elastic deformation.

 

[Janger]

I’m just trying this with 0.375” 6061 rod.

 

[Dabbler]

I’m just trying this with 0.375” 6061 rod.

Then use an end mill (in blue) to relieve the centre of one jaw, like this to get a 3 point contact.

 

[Janger]

here's my take on this: Make the holes .375 BUT there's a trick to it (there's always a trick)

View attachment 17974

You mill the holes with a .005 to .010 spacer, then after the boring is complete, relieve the holes (shown in red) an additional .020 - this relief amounts to about 15% of the diameter (if you include both sides) when complete. Now there is no way for the jaws to 'pinch' the pin when released, and when you tighten you get positive, repeatable clamping.

I don't quite get it. Sounds like to me I should bore it 0.375 diameter (with the spacer )and then bore it again to 0.375+0.020 = 0.395. Why is that any different than just boring it to 0.395 in the first place? I think I'm missing something.

 

[Dabbler]

it is just to relieve the centre of one jaw, not the complete hole. this form 3 points of contact like this: I'm sorry for not being clear, or illustrating poorly...

 

[PeterT]

Here is another idea to ponder. If you do enough of this gang style CNC machining, maybe it would warrant buying some cheapo drill chucks & mount them to a dedicated fixture plate. The advantage is you could grip a wide range of stock diameter & pop them in & out relatively quick with no special tools. Each chuck would be attached to plate at some fixed, known offset distance, so presumably once you indicate off one gripped reference pin, all the rest would immediately be in alignment. And each part would always be concentric to chuck axis regardless of diameter axis. On the downside, limited length range. I don't think stock can protrude through the backside even on the threaded ones? And runout will probably not be great at that price. OK.... how about v2.0, a gang of ER collet blocks perhaps?

 

[Janger]

A gang of ER collets sounds like an idea.

 

[Janger]

Soft jaw.

 

[Janger]

Cutting out arms

 

[Tom O]

I thought you would have machined the tabs down to about 1/32 1/8”

 

[Janger]

I used the default tab size whatever that is. Big. Smaller next time.

 

[Janger]

Some pics.
Milling parts (clamp standoffs) that could be lathe parts.

Then power tapping on the little manual mill. I bought a couple quality? Sowa taps after I broke my one #10-24 tap in the cnc. Somebody on here said to tap small parts with a drill chuck loosely tightened - then when Issues arise the Chuck just spins without breaking the tap. Kind of a red neck torque limiter. Doing it this way is also really fiddly and slow. It does work as I have not broken a tap so far. At $16 each I’d rather not break them.

 

[Janger]

More
Some assembly.

 

[Tom O]

They are looking good.