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Homemade ER 32 collet chuck for the 9x20 lathe

So we have this nice ER 32 collet chuck that fits into the MT3 spindle of the lathe.  That's great if I want to work on short pieces.  This style chuck as well as the MT3 collets limit the length of stock you can put into them because they do not allow the work to pass through the spindle.    You need a draw bar to hold the chuck / collet in the spindle.  On larger lathes this draw bar is a tube that allows work to pass through the tube and spindle.  There simply is no room for this on an MT3 spindle.

This project started not so much because I "need" another collet chuck but because I wanted to see if I could make one and get good repeatable results.  Hopefully I will increase my machining skills a little and learn more about the finer art of tool making.

For this project i decided to use a 4" backing plate I had ordered as a spare.  Grizzly sells them as part P4000102 a back plate for the 3 jaw chuck.  Price at time I wrote this was $6.25.  A bargain in my book considering the cost of steel and time to make one.  You can pick one up when you order the extra 45 tooth gear for the tumbler reverse project. The first thing I did was clean off the packing grease.  What a mess.  Make sure you get it all, especially in the threads.  I then mounted the back plate and took a light clean up cut to true it to my spindle.  I was surprised how true it was to start with.  Then ran the indicator against it to check my work.  Looked good.  So I removed the back plate and reinstalled it.  Test again. Got the same readings.  OK  This proves I should get a decent repeatable fit each time I use the chuck.

Lets move on to the front part of the chuck.  You will need a piece of 4" (or little more) diameter steel about 2" long.  Mount it and face one end.  Then cut the recess to match the back plate you have already trued up.  Finding this piece of steel could be expensive.  An alternative would be a piece of 2" diameter and a piece of 5/8 or 3/4 plate.  Bore a hole in the plate to accept the 2" piece and weld them together.  Just make sure to get good penetration because you will need to clean up the welds during machining.  Another alternative would be a piece of 2.25" diameter stock.  You could machine internal threads to mount it directly to the spindle, eliminating the back plate. 

In this pic I have reversed the work to prepare the front side of the chuck.  You will need to turn down the 4" diameter to mount your collet nut.  This leaves either a large pile of chips or a nice ring.  I happen to have a 2" hole saw.  I decided not to waste all the steel and remove the excess as a ring.  I took a facing cut.  Then used the hole saw to bore the ID of the ring.  Once I was at the proper depth I removed the hole saw cleaned up the chips and oiled the saw.  Then re-insert the saw to give the work some extra support during the parting process.   A live center would do the same but the saw was already mounted.  :)  Plus it gave the ring somewhere to land when it separated.  Parting went better then expected.  To a depth of about 5/8"  then the chips started to clog the cut and it would jam.  The clutch saved me twice before I changed methods.  I was close and decided to use a hacksaw.  A few minutes later I ended up with this pic.  Pretty slick.  What will I do with this ring?  Don't know perhaps part of a ball turner? face mill? 

Parted and drilled


We have the basic shape of the chuck now we need to mount it to the back plate.  I don't own a rotary table or dividing head.  Decided to use the back plate and a center punch to mark the bolt hole locations.  Parts clamped together so they don't move when I punch the holes.   As I discovered later it was good I did it this way.  The holes in the back plate are not evenly spaced.  They will only line up one way.  Using a dividing method to space 3 holes 120d apart would have caused some grief.  At least this way I can't put it together wrong and get it off center.  :)

Center punch the chuck using back plate as template.


Set up on the mill For drilling and tapping.  Center drill, drill to 1/4", then final drill.  I decided to use the same SHCS (socket head cap screws) as are in my 3 jaw chuck.  They are M8 x 1.25 x 20 mm.  I had the tap from the QCTP project.  If you don't then 3/8 x 16 x 3/4 or 1" will do.  You will have to enlarge the holes in the back plate though.  Yes I used the mill to power tap the holes.  Each hole was done 1 at a time.  This involved several bit changes for each hole but does mean I get good tapped holes.


Progress so far.  Chuck mounted to back plate.  OD of chuck turned to match back plate.  The 4" diameter flange of the chuck is about 5/8 thick before clean up.  The stub is about 1 7/8" diameter before cleanup.  Not sure if I should finish the threads for the nut or bore and set the taper for the collets? 

Chuck mounted to back plate


A pic showing the way I set up for boring the taper.  Mounted the ER32 MT3 holder with a collet and bar.  Then put a second collet on the bar.  Adjusted the compound slide to match the taper of the second collet.  This got me close.  Once done I removed the bar and collets.  Used the taper in the MT3 collet holder and a dial indicator to fine tune the compound slide. 

This pic shows final pass on the boring job.  As you can see I have already cut the threads.  That was a standard threading job.  Just use the collet chuck nut as the test gauge.  Once it spins on with a little resistance STOP threading.  Final bore was pretty smooth all things considered.  The test will be how well it performs. 

A test bar mounted in the finished collet chuck.  I get 0.003 run out.  Now this could be my test bar.  I need to find / make a good known test bar.  :)  Everything seems to tighten up well.  I can reproduce that 0.003 run out by moving the test bar around.  Even though the bore is smooth and the collets seem to seat well I think I need a tool post grinder to take a final pass on the bore to finish things off.  Some testing to date shows it works well.  Will see how the long term holds up.  

You can see in the pics above I left a step behind the threaded portion.  This is where I have drilled 3 holes the same size as the ones in the lathe spindle.  I install a tomy bar in one of these holes when tightening the collet nut and a second bar in the spindle to remove the chuck.  It was fun removing the chuck before I did this.  :)  Strap wrenches come in handy for these things.   

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