Threaded Mandrel for Unimat SL Chucks

[Paul Jones]

This is an easy project for making a threaded mandrel. This mandrel is for using a very small chuck on larger swing lathes. The small chuck is from my Unimat SL lathe with a 3” swing.

This mandrel shank is 13/16” in diameter by 1.5” long and fits my largest-sized ER32 collet for my 7” swing mini lathe. The mini lathe is used almost exclusively for small collet work and adding the small Unimat chuck can be allow more holding options. The mini lathe collet chuck can be adjusted to run true on the lathe spindle and this why it is used for small and precise turning.

The mandrel was machined from 1” diameter 1144 Stressproof Steel and a die cut the M12X1 threads. The profile is an exact match to the spindle profile on my Unimat SL lathe.

This threaded mandrel fits into a 13/16 ER32 collet (one of the largest sizes of ER32 collets)



Mandrel installed into the 7" swing mini lathe collet chuck



Unimat chuck installed on the mandrel



Also possible to install an ER16 collet chuck but not really necessary with the ER32 chuck



Two construction photos machining the mandrel to exactly 13/16" diameter using my 12" swing geared-head lathe. I consider the machining performance of this 12" swing lathe is very good after making several adjustments and mechanical improvements (see my other postings for the lathe).





Thank you for looking

Paul

Post Script:

Started to use the Unimat chuck on the mini lathe and found the mandrel required a thru hole just like the spindle of the Unimat SL 1000 lathe.

Before starting to drill with a center drill, the mini lathe ER32 collet chuck, 13/32 collet and threaded mandrel were adjusted for a TIR of 0.0005" (which is about as good as it gets with this circa 1993 mini lathe with its original headstock bearings). The collet chuck allows up to 0.003" TIR adjustment by loosening the three spindle clamping bolts and nuts (but keeping still very snug), and use a soft faced hammer tap the collet chuck housing until the chuck runs true as measure with a dial indicator with 0.0001" graduations. Then systematically tighten the three bolts while checking TIR with the DI. This sounds easy but it does take a light touch with the hammer and several iterations to reduce the TIR measurements.



The thru hole was drilled out to a final ID of 9/32" (~0.281") to match the Unimat spindle thru hole.



The newly drill hole was deburred by hand.



The photo of the finished mandrel with a the new thru hole.



Again, thank you for looking at this update, Paul Jones, April 2, 2016

[DIYer]

Thanks Paul Jones! We've added your Threaded Mandrel to our Lathe Accessories category,
as well as to your builder page: Paul Jones's Homemade Tools. Your receipt:

Threaded Mandrel by Paul Jones

tags: lathe, chuck, mandrel

[PJs]

Thanks Paul. Nice addition to your kit! For some reason I thought your ER set for the mini lathe was a spindle type. Does the flange type use as much bed length as a chuck? My 4" with flange uses another inch compared to the 3". Like the versatility of not having to break down your ER set up to go back to a chuck but looks like you lose about 1/2 bed length when all attached. Nice turn dimension there!! I like the 1144 stress proof also, especially on the mini. Thanks for sharing your build...simple great addition to your capabilities! ~PJ

[Paul Jones]

Thanks PJs. I published this simple machining project just to get the discussion going about using collet chucks in lathes. I made a comment the other day on one of the machining YouTube channels about where did the author buy the very simple 5C collet chuck for his lathe. One of the other viewers joined in the discussion and told me how to make one to fit in the MT5 taper on my 12" swing lathe by machining an unhardened MT5 to MT3 adapter. It was a great idea.

I am now considering making a 5C collet chuck for the 12" swing lathe by starting with an unhardened MT5 to MT3 adapter and boring the center larger and adding the 10 degree taper for 5C collets. I can make a simple threaded draw bar with a recessed shoulder to allow knocking the collet back out of the spindle. I think this will be an inexpensive way to add 5C collets to the lathe.

Back to you question, my import mini lathe (bought in 1993) has a MT3 taper in the spindle but it also uses the typical flange on the spindle for bolting the chucks and faceplate onto the spindle. You can take advantage of this way of attaching collet chucks to eliminate a lot of the TIR. Several years ago I bought the ER32 chuck from Little Machine Shop and the collet sets are a very good quality from Techniks (very low TIR). Most of the ER32 collet sets go up to 3/4" and I added the 25/3" and 13/16" sizes.

The chuck mounts to the spindle flange with three bolts and nuts. In practice the recess in the back of the collet chuck is machined to an exact fit over the spindle flange for a quick way (well not exactly "quick" when dealing with the loose bolts, lock washers and nuts) to mount the chuck. Instead I machined the recess in the back of the collet chuck to be about 0.003" larger in diameter. This allows adjusting the chuck to run true on the spindle using a gage pin in the collet, a dial indicator, snugged bolts and and soft hammer to make the adjustments. This works well for me when dedicating the lathe most of the time to collet work. Most of the work is for short parts so loosing an inch of working room is okay and could use steady rest. The longer work is performed on the 12" swing lathe with 37" between centers and its steady rest.

Regards,

Paul

[PJs]

Great that you are bringing the collets to the forefront. I've had the LMS spindle set on my wish list for a long time now and appreciate the feedback on quality. I found a 18pc set of German made ones with spindle holder and wrench for ~$130 on ebay a while back but he sold out, and I had other things to take care of. They have a US subsiderary to buy direct from up in Portland or Vancouver...just not positive they aren't metric equivalents¿ They have a 1/2" draw thread but like you say it's a pretty easy make. Still would need a 3/8-16 for the LMS. Either way Collets of any type are on my wish list for sure.

I get the flange Idea but like the extra bed length...hence my 14" if I ever get it done. The idea of boring the backing plate 3 thou over is real good. Been thinking about Mr. Pete's video a while back about the expensive centering 3 jaw chuck he put on his Hardinge and wondering if a cam type shoulder screw could maybe do a similar job on the peanut?? A 5C spindexer has been on my list as well but a set of collets are twice the price of the indexer but give lots of opportunity for lots of uses.

Personally I still prefer the ER32's even with the size limitations, as I have experienced them first hand when I designed and built the "Drill Machines" to the tolerances I had to work with. I used them on the 4 Desouter electro-pneumatic drills used on the headstock. The largest used a 1" insert type ball end mill into stainless, inconel and hasteloy. The 2 small drills used carbide circuit board drills...never an issue running 2 shifts for about 6 months then back to 40 hours for years as far as I know.

Great Idea on the unhardened MT reducer...can't wait to see how it works out. Good Luck and thanks for the quality topic! ~PJ

[Paul Jones]

PJs,
I agree with preferring the ER class of collet with their 1 mm clamping ranges (~0.04") and better holding qualities. However, I think there is a larger selection of new and used fixtures based on the 5C collet, plus the ability to customize the collet (soft jaws), expandable versions to clamp ID, and ones for hex and square rods. I don't think you can have too many different collets but having the common diameters is really all you need. Thank you for the advice.
Regards, Paul

[PJs]

Paul,

Totally agree with you on the long term versatility and availability of 5C collets and the holding systems available or build-able. I've not seen or heard of hex/square stock 5C but will look into them, Thanks.

I don't think you can have too many different collets but having the common diameters is really all you need. Thank you for the advice.
Regards, Paul

Here, here, never too many tools or makes. As for the advice...hope it didn't sound like that, just musings from the peanut gallery and the way back machine. Every tool has a purpose the more the better IMHO...kind of like a good pocket knife. Always appreciative of what you bring forward. Thank You!

[Paul Jones]

PJs,

I like to know more from your "way back machine" such as your machining of stainless, inconel and hasteloy. That statement got my attention because few every talk about inconel and hasteloy. The materials are expensive and you don't get too many machining passes do experimenting cuts and get it right before reaching the final pass.

Yes, the 5C collet system has many versions to hold different types of cross sections and come in Imperial and metric dimensions. I especially like the expandable collet design to hold parts by the ID just like an expandable mandrel but much faster with the open and close cycles.

Thank you for participating in the discussions.

Paul

[PJs]

Thanks Paul, I contacted Peabody on the Inconel and Hastelloy but even his memory has some slippage. Not sure how much they are actually used anymore because of the exponential strides in material sciences but yes they are a bit tricky and unforgiving to work. Mainly they are used in high heat, nasty (corrosive) environments as you probably know from your background, primarily because of the high nickel/chrome content. Hastelloy has moly/tungsten as well and maybe more challenging to work than Inconel in conventional machining operations.

In this case it was to work tubing of various diameters and wall thicknesses. Part of the reason for successfully working these materials was the Desouter drills were driven by VFD's fed by code (RS-485) and had the ability to peck and dwell by code as well. The difficult thing was to figure out the speed/feed/peck and dwell for each operation, material and size/wall. I developed a spreadsheet the size of Rhode Island, barely legible on "B" size paper and probably 10+ sheets, for all the tools and operations so I could develop the code...but I digress.

Basically I could develop a starting place for each op mathematically, but as we all know its only a starting place to hone in on the requirements. So I did a bunch of tests on small pieces until I could get the desired results, clean hole sizes, finishes and accurately placed. The 1" and 3/8" insert ball end mills were Kennametal and I spoke with their AE (applications engineering) people to get the right inserts for those two materials, to get a modicum of life out of them. They were coated Tialn if memory serves, but may have been Ticn. There was also medium size drill that I used carbide end mills on to create a flat and port. The carbide circuit board drills on the small drills held up pretty well once I got the feed rate dialed in and spun them pretty fast ~10-15k because they were small and 4 flute, IIRC. They would eventual fatigue and bink, but cheap compared to the inserts for the ball end mill which held up really well over many, many runs. And as a bonus, the inserts worked wonders on the stainless, Al and CU runs which were more common. The 5 materials and all the sizes were the real challenge to speed/feed, to peck or not to peck and try not to dwell on it to keep the machine speed up.

Bottom line for Inconel and Hastelloy IMHO, is multiple pecks and a light (short) dwell at the end for a finish and good, Solid work holding...with the right tooling of course, including the ER 32 collets to hold them. Also I had built in a flood coolant system to help flush and cool. Don't remember the coolant type, only trying to get people to change it regularly! @¿@ Nothing like the smell of bad coolant on a hot afternoon. That was 3 years of 50-80hr weeks for Peabody and way back machine in a few paragraphs. Hope that helps.

Yes, the 5C collet system has many versions to hold different types of cross sections and come in Imperial and metric dimensions. I especially like the expandable collet design to hold parts by the ID just like an expandable mandrel but much faster with the open and close cycles.

I also like that ID/OD holding feature for collets. Way versatile! This Old Tony has some collets for his lathe that I think he shows in his CNC build(?) that are quite interesting and appear they would be quite accurate by design...but old school I think...worth a look.

Always enjoy your threads...Peabody too! ~PJ

[Paul Jones]

PJs,

This discussion proved to be very useful and I am sure everyone has learn something new. I sure did. I will check out the video by "This Old Tony". I have been watching his channel after hearing Dale Derry (YouTube Channel Metal Tips and Trick) recommend this channel. By the way, I just started watching the YouTube channel "James A. Lea The Village Clockmaker" (see https://www.youtube.com/channel/UCWm...GuJvivB73YedFw ) and this type of small lathe and machine tool work is something I like to do. I think you will enjoy watching it and especially watch the second oldest video about his shop tour.

Thanks again,

Paul