|ER-40 Collet Chuck mounted on the lathe|
Every time I get to use my JET 1024 Lathe I have a hard time wiping the grin off my face. The machine is very sturdy and accurate for its size, and has served me very well so far, but has a few minor annoyances. For example, the spindle has a straight 1.25" bore with no Morse taper. Recently I had to make a few dozen studs for a steam engine project using a 4-jaw chuck where using collets would've been much more efficient and convenient. Since using collets in the spindle is out of question, the only option left is to use a collet chuck, so last month I set out to either make or buy one. After going back and forth between C5 and ER-40 I ended up choosing ER-40 for various reasons.
The original plan was to buy the nut and make the chick body from scratch but it posed a few challenges. First of all my lathe doesn't [yet] have the change gears to cut metric threads, and all of the nuts I found used M50-1.5 thread. While there are taps available in that size, they are pretty expensive, costing close to $100 (USD). More importantly, the chuck would need to be hardened and have the taper ground while mounted on the spindle. I wasn't sure I was up for that challenge, so the plan was abandoned pretty quickly. A more viable option was to find a ready-made ER-40 chuck for the lathe, or at least something that would be hackable into one.
After some searching I found a seller in the UK, Gloster Tooling, that sold an ER-40 lathe chuck/fixture on eBay for roughly $100 + $36 (USD) shipping. The price seemed reasonable, and my only reservation was that I didn't find any reviews of the company or this chuck, which looked like a Chinese import. Alternatively, I found a seller on Amazon that offered ER-32 Collet Chucks and ER-25 Collet Chucks , costing roughly half of the Gloster's offering. Eventually I decided that the extra capacity of ER-40 collets was worth it for me, so I placed my order on January 30th and received the chuck in 9 days afterwards. It came in plain cardboard box, wrapped in a piece of cellophane and padded with two small pieces of styrofoam with no paperwork or mounting hardware. It looked pretty much like any other Chinese item I've ordered, except it came from UK.
|ER-40 Collet Lathe Chuck|
Overall the finish wasn't bad; the threads were cut very nicely and the nut action was silky-smooth. All-in-all the chuck looked promising so I decided to check the runout. To do so I turned a piece of aluminum down to exactly 1" in diameter and without removing it from the 3-jaw chuck, tightened 1" ER-40 collet around it using the new chuck (as shown in the picture).
|A piece of aluminum turned to 1"|
Using a dial test indicator against the register's rim I measured about 0.0007" of runout. To make sure that the runout is not coming from the collet, I turned the chuck by 90 degrees while keeping the collet in place; the runout staid about the same. In contrast Bison's C5 chucks state their TIR to be 0.0004", or a bit over half as much but for the price I can't complain.
|ER-40 chuck showing less than 0.001" runout|
Now the chuck has been deemed "worthy" the real fun part was about to begin. My lathe came with a bastard M49 x 8 TPI thread*. To my knowledge nobody makes a backplate for that thread, so I had to make one from scratch. Before proceeding though, I had one last thing to do: make a copy of the spindle thread. On the third try, after cutting the first threads too deep and second threads at a wrong angle, I finally made one that was spot-on.
|Copy of the spindle machined out of a piece of aluminum|
Yes, you've read it right: 49mm metric thread with 8 TPI pitch. Apparently JET sourced their 1024 lathes from several Taiwanese manufacturers back in the '70s, and the concept of standardized threads was pretty foreign to them, apparently.
The backplate should be made out of cast iron, since it provides good vibration dampening and, being a metal dissimilar to the spindle, is unlikely cause galling. The least expensive option I found was ductile cast iron from McMaster Carr. They sell it by inch, but unfortunately the smallest diameter available was 6" (a bit over 150mm).
|4" Chuck sitting on top of a 6" chunk of cast iron|
There was a lot of material to remove. To save the tools (and some cast iron) I traced the outline of the chuck on one side of the disk and trimmed the excess on the bandsaw. The rest was up to the lathe, and after several nerve-racking hours I machines my first backplate and cut my first internal 8 TPi thread.
|Finished threaded back plate for the 4" ER-40 Collet Chuck|
As a side note, cutting such coarse threads in cast iron turned out to be pretty exciting. Even with when advancing the cross slide only a few thousands at a time, my 0.75" boring bar was visibly flexing and chattering, so the threads didn't turn out as clean as I wanted. I paid extra attention to the register, which ended up fitting perfectly. As a result, the backplate ended up being very repeatable.
|Mounted chuck shows less than 0.001" of runout|
Once the chuck was mounted on the spindle I rechecked the runout again, this time without the collet, and was pleasantly surprised to discover only 0.0005" of runout, even after screwing and unscrewing it several time. All in all I'm very happy with the result. My total cost, including the back plate material, was around $180 (USD) or so, which is not that bad in the great scheme of things.