Author Topic: Building a New Lathe  (Read 155446 times)

RobWilson

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Re: Building a New Lathe
« Reply #200 on: May 06, 2015, 02:11:33 PM »
 :bow: :bow: :bow: :bow: :bow: now thats looking real canny Steve   :clap: :clap: :clap:


Rob  :thumbup:

Offline Manxmodder

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Re: Building a New Lathe
« Reply #201 on: May 06, 2015, 02:19:55 PM »
Yep,it looks a top job,Steve.  I'm well impressed with the standard of workmanship :bow: ,it's going to be a great asset when finished....OZ.
Helixes aren't always downward spirals,sometimes they're screwed up

Offline vtsteam

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Re: Building a New Lathe
« Reply #202 on: May 06, 2015, 02:29:05 PM »
Thanks Phil! Roller bearings. I bought a new replacement spindle and matching bearings for a mini-lathe early in the thread, so will install those together in the headstock when the time comes.

(The lathe is just sitting on the feet now, not attached. Had to lift it up to higher to attach the apron.)

Thanks Rob, Oz!  :beer: :beer:

I love it when a Plan B comes together!
Steve
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Offline Brass_Machine

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Re: Building a New Lathe
« Reply #203 on: May 06, 2015, 03:45:15 PM »
Yup. That is looking good. I expect it will  out perform the Asian minilathes (like mine) without breaking a sweat!
Science is fun.

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Offline vtsteam

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Re: Building a New Lathe
« Reply #204 on: May 06, 2015, 09:05:57 PM »
Thank you Eric! I hope it will last me as the main machine for as long as I can make things -- if I'm lucky that's still a while yet. So I'm trying to make it solid and accurate, within my capabilities. If it looks any better than earlier stuff that's Rob's fault, because his work always makes me try to do better than I have so far.

And of course the encouragement people here are so generous with and the inspiration of their projects keeps me going back to the shop to make things and put up pictures.

Things don't always go well, of course, I had a disappointment this afternoon in trying to make a tap for acme 1/2" - 10 TPI. These cost $50 if you can find them. That's hard to justify, especially since I need to save for a chuck eventually.
So I've been collecting info on tap making.

I tried a method I saw on another forum after a web search, which showed a tap made by simply grinding 4 flats at the end of some threaded rod, set at a taper of about 30 degrees. This just didn't work for me. I tried it with various angles, and unhardened and case hardened (with kasenit) on a scrap piece of aluminum, I simply couldn't get it started. It would just chew up the aluminum and wobble out of line. I don't know what I was doing wrong.

Seems to me the thread is just too coarse for this kind of tap, even though the reference I read said acme taps made that way had been successful. The picture though in the post was of a very fine thread 60 degree tap, and the example had cut into brass, which I think would thread much cleaner and crisper than aluminum.

So tomorrow I will probably try again, but this time attempt a conventional machined tap, turned on the lathe to an entry taper, with flutes, and some rake angle.  And I'll case harden it from the start.

So, fingers crossed it will cut zinc alloy cleanly.

I love it when a Plan B comes together!
Steve
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Offline awemawson

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Re: Building a New Lathe
« Reply #205 on: May 07, 2015, 02:13:19 AM »
Steve, tapping coarse acme threads, I've always bored and threaded them undersized in the lathe then used the tap as a finishing pass.
Andrew Mawson
East Sussex

Offline PekkaNF

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Re: Building a New Lathe
« Reply #206 on: May 07, 2015, 03:11:45 AM »
Once I was thinking of buying a tap roughly same size trapezoidal thread 12 mm and 2 mm lead....One Brittish tap maker I called said that that they would need to charge about 140 of it, it needs to be long, cut gradually and all in all it is hard to make one that will work manually and will not break.

I have been reading of people drilling oversize hole, using normal V-thread tap (same lead) to remove some metal firs. I believe it's not too easy.

Also that size internal threading will not be easy. When you substract thread part out of the diameter, there is not much left for threading bar core diameter.....Would probably need to be as short as possible and you many need to to make two bars to optimize thickness and cutting tooth lengt - bit like first cut / second cut tap. Helix angle and all. Did not want to go there

So, I'm designing that part a little fatter to make room for ready made nut. Left handed nut and trapezoidal bar are not cheap, but cheaper than the alternative.

Pekka

Offline awemawson

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Re: Building a New Lathe
« Reply #207 on: May 07, 2015, 03:25:25 AM »
Have you considered a quashed Acetal nut?

Never done it but some swear by them - turn / bore your plastic blank with a core sized hole, place in suitable outer clamp over the acme male thread and warm and tighten. The plastic flows around the thread. You can then turn the o/d to suit. I believe a dusting of graphite powder is used on the male

http://bbs.homeshopmachinist.net/archive/index.php/t-43645.html
Andrew Mawson
East Sussex

Offline Pete W.

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Re: Building a New Lathe
« Reply #208 on: May 07, 2015, 04:27:39 AM »
Hi there, Steve,

This project is looking very impressive so far.

Regarding your problem with taps, I've just clicked my way through about twenty pages of the Model Engineer forum until I found this:

  http://www.model-engineer.co.uk/forums/postings.asp?th=103007&p=28 

I knew it was there somewhere!  I hope it helps. 
Best regards,

Pete W.

If you can keep your head when all about you are losing theirs, you haven't seen the latest design change-note!

Offline Will_D

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Re: Building a New Lathe
« Reply #209 on: May 07, 2015, 05:36:52 AM »
What about a multi-stage casting process to end up with bronze nuts?
Engineer and Chemist to the NHC.ie
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Offline vtsteam

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Re: Building a New Lathe
« Reply #210 on: May 07, 2015, 07:44:17 AM »
Thanks Pete, Will!  :beer:

Will, In this case I need to tap the casting. It's a little different than the usual method of a cross slide leadscrew nut. Gingery style. Anyway, can't cast for this particular job, and impractical to internal thread on the Craftsman with the amount of overhang, so a tap, either made or purchased is the right tool for the job. Later I can cast nuts with threads, and will do that for sure with the half nut.

Pete, thanks. Those taps have a really long taper, which is probably a very good way to do it, I'm thinking. The problem yesterday was, I believe, too short a taper, and too shallow a rake angle -- which is a result of the particular unusual way of making a tap. Apparently it is a very old way of doing it -- but I just think t's not good for a coarse acme thread, and maybe my practice piece of aluminum wasn't th best choice to try it out on, or maybe these need a big clearance hole and have low thread engagement.

I don't know what was wrong in my case, because I do believe that the person who recommended it was successful in cutting acme threads. One of those cases where you have to see the tap and operation to know what was different about it from what you are doing, rather than just read a word description.

Well today, more tap experiments.......
I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Building a New Lathe
« Reply #211 on: May 07, 2015, 08:31:23 AM »
Oops, missed your replies Andrew and Pekka -- thanks for the suggestions -- and as I said this isn't tapping a nut, but the operator end of the carriage casting itself.

Pekka your tech description is helpful. I just remembered that I do have an acme tap, a 1" x 6 TPI (I think) , and it works fine, so I'd like to take a close look at that, check the rake angles, taper angle, relief, etc. since it cuts great. I made a drive nut for my horizontal mill with it in steel, just hand tapping. Seems like 1/2" x 10 should be a piece of cake by comparison, with the right tap.
I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Building a New Lathe
« Reply #212 on: May 07, 2015, 08:44:13 AM »
Here is one site I was looking at for tap making info.

http://mckgyver.pbworks.com/w/page/20654129/AcmeTap

Notice that the chart shows the tap rake angle as low as 0-3 for cast iron, and relatively low for brass (just as we typically reduce top rake angle for lathe tools, and flatten drill lips for that material) but relatively high rake angle for aluminum and zinc die castings.

That makes me think that the first tap I made, following the old style 4 bevel end on a coarse thread produces a very low rake angle, and while it might work for finer pitches in brass (as shown on the forum post I saw) or cast iron, would definitely not work with coarse acme in aluminum.

Since the ultimate use will be on zinc, I'm going to say a 10 degree tap rake angle would be minmum, according to that chart.
I love it when a Plan B comes together!
Steve
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Offline Pete W.

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Re: Building a New Lathe
« Reply #213 on: May 07, 2015, 09:18:39 AM »
Hi there, Steve,

The tap-making whose link (another Andrew!) I posted earlier was for a square thread, I guess acme ought to be easier.  I don't think he intended to cut many threads with his taps - his project is steerinng gear for a pair of traction engines (but quite big ones!!!).

Did you specify Right-hand or Left-hand, or did I miss that?

If all else fails, there's a firm here in the UK that sells Acme taps of feed-screw sizes to the Model Engineering market, I'd be happy to act as 'go-between'. 
Best regards,

Pete W.

If you can keep your head when all about you are losing theirs, you haven't seen the latest design change-note!

Offline vtsteam

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Re: Building a New Lathe
« Reply #214 on: May 07, 2015, 09:46:10 AM »
Thanks Pete, will try making one before buying -- pretty sure I can get them here, if need be. Right hand, so not too unusual.

I've been playing around with a drawing and one way of cutting the flutes to get a 10 degree angle might be to just offset an end mill from center and cutting to a specific depth -- at least it works out on "paper."

In this case, bring the edge of the mill in .155 from center, then mill to .293 depth. That should yield 10 degrees tap rake angle:

(Interestingly, the .293 depth determines the rake angle, the .155 just determines how much clearance you get -- I just guessed .094" might be enough for the tooth depth. Tapering the end of the tap just reduces clearance, but doesn't alter the tap rake angle  -- it is determined throughout by that .293 cut.)

There is no backed off relief in any of this -- hoping it will work well enough wihout it -- fingers crossed....

I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Building a New Lathe
« Reply #215 on: May 07, 2015, 12:46:25 PM »
Cutting:

« Last Edit: July 11, 2017, 03:50:36 PM by vtsteam »
I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Building a New Lathe
« Reply #216 on: May 07, 2015, 12:48:02 PM »
Fluted and stub squared:

« Last Edit: July 11, 2017, 03:51:05 PM by vtsteam »
I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Building a New Lathe
« Reply #217 on: May 07, 2015, 12:49:22 PM »
Case hardened and tempered:

« Last Edit: July 11, 2017, 03:51:33 PM by vtsteam »
I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Building a New Lathe
« Reply #218 on: May 07, 2015, 12:51:10 PM »
Test cutting some chewey aluminum scrap:

« Last Edit: July 11, 2017, 03:51:59 PM by vtsteam »
I love it when a Plan B comes together!
Steve
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Offline vtsteam

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Re: Building a New Lathe
« Reply #219 on: May 07, 2015, 12:52:52 PM »
It works!  :thumbup:

« Last Edit: July 11, 2017, 03:52:23 PM by vtsteam »
I love it when a Plan B comes together!
Steve
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Offline awemawson

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Re: Building a New Lathe
« Reply #220 on: May 07, 2015, 01:34:17 PM »
Excellent Steve - and the zinc alloy should tap (hopefully) even better. What sort of finish did it leave on the aluminium?
Andrew Mawson
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Offline vtsteam

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Re: Building a New Lathe
« Reply #221 on: May 07, 2015, 02:13:58 PM »
Okay, Andrew, but not as nice as the zinc. I just tapped a leftover zinc mini-muffin ingot from last pour to see what the thread looks like - here's a close-up:



And the fit on the rod is pretty darn close. probably because a section of the rod was used to cut the thread. When I screwed one of the three foot rods in, it has only about a quarter inch of side play at the far end with the ingot clamped in the vise. Almost no play at all. But it's also an easy smooth turning fit. Basically it's a custom made thread to the rod.
« Last Edit: July 11, 2017, 03:52:49 PM by vtsteam »
I love it when a Plan B comes together!
Steve
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Offline PekkaNF

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Re: Building a New Lathe
« Reply #222 on: May 07, 2015, 03:43:08 PM »
Looking good.

The way you did the "rake" looks good, I startted think of it and I think that if you make "hook" it will change effective shape of the cut. Me thinks. :scratch:

Pekka

Offline vtsteam

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Re: Building a New Lathe
« Reply #223 on: May 07, 2015, 05:06:23 PM »
Not sure what you mean Pekka.  No matter what shape the flutes, the screw can only make its own shape in another solid. A different shape flute relief will affect the ease of cut, only.

Commercial taps have radiussed relief cuts mainly to reduce notch sensitivity I believe, so the tap will break less easily.
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Steve
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Offline modeldozer

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Re: Building a New Lathe
« Reply #224 on: May 08, 2015, 04:29:10 AM »
Well done.  Filed away for in case.  :clap: :clap:

 :beer:
Abraham