ER40 Chuck Pin Spanner

[WobblyHand]

A while back I made a back plate for my Shars ER40 Collet Chuck. I still don't have a good way to tighten the collet nut properly. I can't quite grasp the chuck in a 5" 3 jaw chuck so I could drill in on my mill. If I could do that, then I could use a simple tommy bar to restrain the chuck while tightening the nut. There is no back gear, nor a lock on my lathe, so I need to come up with something. Staring at the chuck reveals there are 4 holes, spaced 90 degrees apart. These are 8mm in diameter and counter bored to 11mm deep. So I got the idea that I could make a pin spanner wrench.

The drawing Shars provides, does not call out these holes. However, I contacted Shars and they provided me the dimensions. 71mm bolt circle, 8mm OD counterbore to 11mm, 6mm through. Armed with this information, thought it was possible to make a wrench. I didn't want to make the wrench out of raw stock - mostly because I would have to buy it. Looked around and the answer was staring me in the face. Just modify an ER40 collet nut wrench. So I found a cheap wrench on Amazon that got me nearly where I needed to be.

I thought this wouldn't be that hard. Mmm, it is tougher than I expected. It's more confusing than I thought. I need enough meat in the wrench to hold the pins. Eventually modeled enough of the existing wrench to determine how to do this. There's not that much clearance to things. The wrench is 6mm thick, the pins can only stick out about 6mm, because the collet nut is being tightened towards the chuck. I think there is about 14mm when the nut is tightened, but need to check. Wouldn't want a wrench that gets stuck by the tightened nut!

"Basically all I need to do is drill two holes that are the right distance apart and press in two pins." I suspect there will be more to it than that! Was thinking of using some dowel pins, but as I recall they are hardened. I also am treading new ground by pressing the pins into steel, haven't done that before. I have some 3/8" OD 1144 rod I can use for the pins. I can turn it to 7.5mm for 6mm length and 8.01mm for 6mm length. Have a 0.3135" reamer to use, which is 7.975mm, which is 0.001" under 8mm. Think I will make a practice piece just to test pressing the pins. I have some 1/4" steel plate which ought to be similar enough to the tool itself.

I will probably grind off the ears of the wrench back near to the pins, but first, lets practice pressing a pin into steel.

 

[darkzero]

I can't quite grasp the chuck in a 5" 3 jaw chuck so I could drill in on my mill. If I could do that, then I could use a simple tommy bar to restrain the chuck while tightening the nut.

Since you mentioned the 5" 3-jaw, sounds like you have a dividing head, rotary table that can be mounted vertically, etc. Not sure what is preventing you from holding the ER chuck plate in your 3-jaw. 5" 3-jaw should be able to grip on to the external threads for the collet nut (use soft jaw protectors of course to protect the threads).

If you're not comfortable doing that another option is stick a 1" dia bar in the collet chuck then you can grip onto the 1" bar with the 3-jaw to drill & ream the radial holes. Use a machinist's jack if you get deflection. If you don't have a 1" collet you could use smaller but the bigger the better.

My ER40 plate (not Shars) came with 3 radial holes & I made a tommy bar to hold it. I personally like the simplicity of using a tommy bar (even though I could use my foot brake) & the same tommy bar fits my super spacer although not really need much for that. Much less bulky than having a second wrench.

But good idea on making a wrench to make use of the holes on the face if you already bought it.

 

[rabler]

I'm probably missing something, but you should have the spanner wrench for the spindle. Does that not work to hold it? Are you trying to put something in the collet before mounting it on the lathe? Or worried that the loosening the collet nut will loosen the whole collet chuck if you hold on the spindle?

 

[WobblyHand]

Since you mentioned the 5" 3-jaw, sounds like you have a dividing head, rotary table that can be mounted vertically, etc. Not sure what is preventing you from holding the ER chuck plate in your 3-jaw. 5" 3-jaw should be able to grip on to the external threads for the collet nut (use soft jaw protectors of course to protect the threads).

If you're not comfortable doing that another option is stick a 1" dia bar in the collet chuck then you can grip onto the 1" bar with the 3-jaw to drill & ream the radial holes. Use a machinist's jack if you get deflection. If you don't have a 1" collet you could use smaller but the bigger the better.

My ER40 plate (not Shars) came with 3 radial holes & I made a tommy bar to hold it. I personally like the simplicity of using a tommy bar (even though I could use my foot brake) & the same tommy bar fits my super spacer although not really need much for that. Much less bulky than having a second wrench.

But good idea on making a wrench to make use of the holes on the face if you already bought it.

I didn't think of using a 1" collet and grabbing the bar. Good idea. Didn't want to grab the threads, even with jaw protectors. Unlike my cheap ER32 collet chuck that I had for my mini-lathe, the Shars collet chuck doesn't have holes for a tommy bar drilled.

 

[WobblyHand]

I'm probably missing something, but you should have the spanner wrench for the spindle. Does that not work to hold it? Are you trying to put something in the collet before mounting it on the lathe? Or worried that the loosening the collet nut will loosen the whole collet chuck if you hold on the spindle?

Since this is a set true collet chuck, once I have dialed it in, I don't want the chuck to move relative to the back plate. The spindle spanner wrench doesn't prevent that. The mounting holes are kind of big and sloppy on the chuck, 9mm for a 8mm bolts. It's kind of like plumbing, you want a wrench on both sides of the two fittings, not one wrench on the fitting and another 4 inches away. I did try using the spanner and the chuck moved a little - and that is not what precise things should do.

This is actually a pretty easy little job. The wrench was cheap - cheaper than I could buy stock for. I turned the pins out of 1144 - that didn't take long. I have the correct size reamer, thanks to @mattthemuppet2 and I have an arbor press. Just did a test pin into some steel plate and it came out nice and tight. The wrench is cheap and as a bonus, it matches the one I already have, so it looks like a set

Had I thought of grabbing a 1" bar in the chuck with both the zero set and the 3 jaw, I would have just drilled a hole in the side. But I didn't. I just plain didn't think of it. This won't be that bad either. The wrenches are flat so they won't take up much room. If I eff this wrench up, I will try @darkzero's idea.

 

[rabler]

Since this is a set true collet chuck, once I have dialed it in, I don't want the chuck to move relative to the back plate. The spindle spanner wrench doesn't prevent that.

Got it, that makes sense.

 

[WobblyHand]

Not full fidelity drawing, but good enough to fab to (he hopes). More or less figured out how to clamp it to the table. Tomorrow's task.
Shop is hot. One of these days I will install a mini-split to moderate the temps in summer and winter.

 

[WobblyHand]

Save for some minor touch up, done. Ground off the ears to make them shorter. Now I can tighten the chuck! Also had to grind off the teeth to get a little extra clearance. Used a file and a dremel for teeth grinding. Didn't take that long.

Here's the set up on the mill table. Not elegant, but good enough to "indicate".


With the holes drilled and reamed. 1/2 of the pins are sticking out. About 0.001" interference.

The pins are pressed in and the ears ground off. Fits in the chuck! What a relief.


The "matched set" of wrenches. "Frick and Frack".


Project done.

If these wrenches annoy me, I can always drill the steel chuck body for a tommy bar. I'll try them for a while and see how I like them.

 

[Doug Gray]

I love your title block in the drawing.