I'm a real machinist too! Well...

[lathesmith]

Okay, maybe not a REAL machinist, but better tinkerer, anyway! (I'm just having a little fun here Buckshot, hope you don't mind). I saw your thread on, well, threads, and you inspired me to share! Anyway, as a Winter project I decided to make a new spindle for my little lathe. The old one only had an .815 thru-bore, and I determined that I could safely get around a .950 + bore--with a new spindle, that is. This doesn't sound like much, but it opens up whole new worlds of machining fun and projects for me. So, I found a nice piece of 4140 steel, and started turning, --and turning, and turning...I think this 3.5 inch piece weighed around 40 lbs to start with, and ended up weighing around 10 or so when done. That is a LOT of cutting! Especially for such a small lathe! I made this thing entirely on my little lathe; I was even able to bore it, with some creative stratagies. While I was at it, I decided a threaded spindle would be handy; so, I determined that 2 1/4-8 would be just right, and that is what I made. I ultimately threaded the new spindle AFTER it was installed, for maximum accuracy. And accurate it is, I am quite astounded at repeat accuracy, actually.
Those tiny threads that Buckshot mastered are impressive. Mine are at the other end of the scale--2 1/4-8 tpi. And, to top it off, I made three backing plates from cold rolled steel, and had to cut INSIDE threads. I did this with a crude but simple 5/16 tool blank that I ground with a threader on one end. It has worked great for several inside projects, and I am amazed at what I have been able to do with this thing! A real personal triumph!
This little lathe is just right for my needs. With a combination of 4 different change gears, I can cut nearly any thread pitch I need. Yes, I know, changing gears is slow as molasses, but this ain't no job shop, it's a hobby shop, and it is perfect for that. I also must admit a dirty little secret--I have equipped this lathe with a 1/2 HP variable speed, fully reversible DC motor and speed control, and this makes threading virtually goof-proof. I love it! Cheating was never so nice!
Thanks to all you machinists (real and otherwise) and tinkerer types for sharing your knowledge and projects on the boards here. Reading about your stuff has given me ideas,and CONFIDENCE to tackle projects (and succeed at them!) that I probably never would have otherwise tried. Thanks again!
lathesmith

[No_1]

I also must admit a dirty little secret--I have equipped this lathe with a 1/2 HP variable speed, fully reversible DC motor and speed control, and this makes threading virtually goof-proof.

I am very interested in this mod, you you explain deeper? I can provide a e-mail address if needed so as not to bore the members here.

R.

[scb]

Very impressive, nice work.

[lathesmith]

No 1, there is really not much to this mod; just replace the original AC motor with an adequate-torque DC or AC variable speed one with matching controller. Actually, I am being a bit modest; I decided to do a self-education on variable speed motors a few months ago, and learned enough to get the job done right. You get the appropriate components on ebay, usually for pennies on the dollar--there is a dizzying array of surplus controllers, motors, and other hardware to choose from. The trick is to know which components will work with what, know your prices and target your auctions. As a cost example, the DC gear I picked up for this lathe only cost me $100 or so on ebay; new, this same stuff is in the $6-800 range. AC stuff is a shade more expensive usually, but it is easier and more economical to go with 3-phase AC to ramp up the necessary power for larger lathes than DC.
And finally, as you can see in the photo, this is not a true variable-speed only setup. I retained my belts and pulleys. Why? Torque! It's easy to get the speed, but to maintain the torque of the original setup would require something like a 3-5 HP variable speed motor without those pulleys. That would be prohibitively expensive, not to mention cumbersome.So, I have not eliminated belt-changing, just reduced it quite a bit. If you'd like more info, I'd be happy to provide some off-board suggestions for a specific project. I don't claim to be an expert, but especially if you have a smaller setup I could probably offer a suggestion or two.
lathesmith

[Buckshot]

...............Lathesmith, damned impressive work all around! Your finishes look superb, and that speaks of carefull setup and consistant feed. BTW, little threads are only hard because they're tough to see. Larger threads are MUCH more difficult to machine then the smaller ones.

Looks to me like you know what you're doing and aren't afraid to try out new stuff. That thread size for the spindle nose was a smart move. There is TONS of stuff on E-Bay for that thread pitch.

..............Buckshot

[Bret4207]

You know what they say about idle hands........

Good job!

[crossfireoops]

Great Job,

Well done, Sir.

GTC

[lathesmith]

I've been thinking about adding a set screw to my thread-on chuck plates. At the moment this doesn't really seem necessary, I never run this thing in reverse at any kind of speed. I guess maybe if I suddenly have the need to cut a bunch of left-hand threads I may need this; but this don't seem likely. Any opinions on this?
lathesmith

[Morgan Astorbilt]

Lathesmith, Good idea. If you decide to do this, use a decent size(dia.) set screw, and don't forget to put a lead(or maybe copper) slug under it, to protect the spindle threads.
Morgan

[Buckshot]

..............If you're going to do that do one of 2 things. As Morgan Astorbilt suggested, put a plug of something between the setscrew and threads on the spindle nose. Or, drill into and just beyond the threads to accept the nose of the setscrew. Also I'd use a good sized setscrew too, say at least 1/4-20. Another thought is use that sized setscrew but make it out of a halfhard brass, aluminum or bronze.

I was thinking the softer setscrews might be good in case of a wreak, yet certainly strong enough for any turning or threading you might do.

.................Buckshot

[Morgan Astorbilt]

The reason I would prefer a soft plug rather than a brass set screw, is that the plug will deform without turning, taking on a relief impression of the thread crest, while a brass screw will deform while turning, perhaps leaving chips which will have to be removed.
Copper plugs for smaller set screws can be easily made from copper ground wire, sizes #4-#8, larger ones from copper rod, which can be bought in various diameters, and can be cut to make excellent soft punches, such as for driving sights.
Morgan

[lathesmith]

1/4-28 is usually my setscrew size of choice, it seems to work for a wide range of applications. If I use one here, that's what I'll go with.
These thread-on spindles have a smooth, unthreaded "chuck register" on the part closest to the sholder near the the headstock. It is around .310 wide, roughly 5/16, on my spindle. This is where a set screw would contact. I figure if I do this, I would need to drill/mill a small indentation for the grub to cinch down into. This is the spot where tolerances are very close, only .001 or so between the chuck adapter and the spindle. A good, tight fit here is what gives good, repeat accuracy for switching chucks and things. NO burrs or raised spots allowed here. The point is well-taken, a set screw bearing down on the threads is an absolute no-no, especially as tight as I have fitted these threads. I think I will probably try my set-up for a while as-is. As one poster pointed out to me on a machining forum, the threaded spindle nose has been the mainstay of lathes for the last century, and the vast majority have worked fine without a grub screw. If it ain't broke....
lathesmith

[JIMinPHX]

These thread-on spindles have a smooth, unthreaded "chuck register" on the part closest to the sholder near the the headstock. It is around .310 wide, roughly 5/16, on my spindle. This is where a set screw would contact...

...a set screw bearing down on the threads is an absolute no-no, especially as tight as I have fitted these threads.
lathesmith

That's good looking job that you have there & a good choice of materials too. I agree that stretching the diameter of your spindle hole can be a big help in a lot of situations that you might run into.

I hope that you will not mind allowing me a few little (hopefully constructive) comments from the peanut gallery over here.

I've had good luck using a nylon pellet or a cross sectional cut from a large 90-duro O-ring as my material under setscrews that point towards threads, although I agree with you that if you can hit an unthreaded area with the setscrew, that is much better.

If you don’t mind me prying with a few questions, I’d like to know just how tight did you fit those threads? Did you measure the Pitch Diameters? Do they sort of get stiff & squeak a little when you tighten them? Did you locate your chuck position on the close fit threads or did you locate on a pilot diameter & just use the threads to pull it all together? I am not familiar with the term "chuck register". Could that be the pilot diameter that I am talking about? If I’m getting too nosey, please just tell me. My inquisitive nature runs away with me sometimes.

[lathesmith]

Jim, I can tell you are the machining type--inquiring minds want to know! There is an unthreaded area, I made around 5/16" long, adjacent to where the shoulder of the threaded backing plate butts up. On the backing plate this diameter is 2.251", or very close to this, as best I can measure with my crude tools. The spindle iteself is 2.250", once again as close as I can measure. Very close fit here, and the threads MUST be in very close alignment to allow this to work. I think this may be what you are referring to as pilot diameter; there are different terms I have seen to apply to this.
I am getting about 5-6 thread engagement, and from the studying I have done on actual pictures and machines, this is about right. I confess, I more or less "made up" my spindle design just based on observation and a few measurements. I waited until I actually had my backing plate before turning the final spindle threads and register. To do this I actually hand-fitted the parts together, by feel, to get the best fit possible. In my experience fitting threads is kind of an art, and this was the only way I knew to get the best fit possible fit. And, by "tight" threads, I don't mean I need a wrench every time I screw parts together. I mean, screw your part on, and the less side-to-side "rocking" that I have, the better the fit. I guess I cheated a bit here too; I used some very fine lapping compound for final fitting together of spindle/backing plate. The backing plate screwed on a bit tight, but after a bit of working back and forth with some 320 grit, high-quality compound the action became very smooth and maintained my very close fit.
I have no way to accurately measure thread pitch diameters, I just had to eyeball it and do it by feel. This takes awhile, I know, but it was a great learning experience and I spent the extra time here, as this is the accuracy of the machine. My work can be no more accurate than I get this part, I figure. Now though, I can dial-indicate a piece, screw the back plate with chuck off the spindle, re-install it, and with my measuring tools I can barely see any changes. This suits me fine, and is good enough for me. BTW, if you look closely at the above pics, you can see the unthreaded area on both the spindle and the back plate that must fit together so tightly.
lathesmith

[JIMinPHX]

Lathesmith, thanks for clearing that up for me. It looks like your chuck register is my pilot diameter. It was just a little language barrier there. Your size & clearance tolerance look to be well chosen. I disagree with you about the necessity for close fit on the threads to maintain chuck accuracy (if I read that correctly). The chuck location should be coming from the mating of the pilot diameters & not the mating of the threads. One of the basics from mechanical design 101 was that locations come from pins or pilot diameters, not threads. Better fitting threads should not be used to pick up location, but they do add greatly to the strength of the joint & the general quality of the job. It looks like you have nice finishes too.

The only down side to cutting snug threads, is that your pitch diameter clearance becomes the maximum T.I.R difference that you can tolerate between the pilot diameter & the P.D. If you buy another backing plate or a faceplate with the “same” thread already in it, you might be in for a rude surprise due to the shoddy workmanship of another. For that reason I always start with a blank & cut my own threads in my backing plates.

The way that you chose to fit up the sizing of your spindle thread is the same as the way that I normally cut the female threads on my backing plates. I get close, then shave a little at a time until I get a snug, but smooth fit. Like you, I prefer the snug fit. I’ve only taken the time to grit lap my threads on a few jobs. It is a real nice finishing method that I usually don’t want to spend the time on. I usually get away with a triangular file followed by some abrasive cloth. I find that to be a bit quicker, although admittedly, not quite as good.

When I cut my spindle threads, I normally measure the pitch diameter using the 3-wires & a micrometer method. If you use rubber bands to hold the thread wires in place, it’s really not that tough & thread wires are not very expensive. The reason that I do this is so that I can then cut a second male thread of the exact same size to use as a fitting plug for future back plates, etc. that I may choose to make in the future. I usually make the gage thread out of something easy to work with, like leadloy or even aluminum since it’s never going to see any heavy forces. I do this because it’s easy to measure the P.D. of a male threads, but measuring it on a female is another story.

[lathesmith]

Right on Jim, you summarize things nicely. I do agree, the threads should not be used to attempt accurate re-location. On precision stuff though, I don't like wobbly and loose threads. I guess I should have clarified this; "tight, but not too tight." And yes, I am nearly certain that other backing plates may need fitting; that's OK though, this is not intended to be a universal fit machine. I made up a couple of extra backing plates, I should have what I need for a long time to come.
That is a good idea to make up a gauge, it can save alot of time when one has several of these to make. BTW, Little Machine Shop.com has the most reasonably priced cast iron blanks I have found, for chucks up to six inches. He carries several threaded ones and has blanks also, and these are all in the $30 range.
lathesmith