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All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Topic started by: OTmachine on February 20, 2021, 10:47:10 AM
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I am looking for a lathe for the basement that is 100% metric. I know that I can get metric transposing gears for an English / American type lathe. But with that there is a progressive lead error as you increase the number of threads thereby having less mate up as you turn the threaded piece into a true metric tapped hole making for a weak fastening. Any thoughts or suggestions?
TIA,
Keith
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LMS has metric threading kits (lead screw, half nuts, new stickers, NO threading dial) for the various lenghts of 7x lathes. But nothing for 9x lathes.
Perhaps look at Canada and UK dealers.
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Good luck, my Harbor Freight 9x19 has the same error for metric threads. Have you checked with littlemachineshop dot com?
I'm sure they will know if such a unicorn exists.
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I've never had a problem cutting metric threads on an American lathe, if it was a thread that the lathe could cut. There are so many fractional sizes in the Metric system that are very close to one another but are not compatible. And even if you had a Metric lathe, being as there are so many fractional sizes it most likely couldn't cut them all.
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I have cut 1 mm pitch threads up to 5/8" long without issue on the mini-lathe (using 21 tooth transposing gear).
But I can certain see the desire for purity and perfection. (At which I frequently fail of late)
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What I am trying to say is that thread engagement is progressively worse which weakens the holding power of the thread. For example: you can start a 1/4-28 screw into a 1/4-20 threaded hole for probably one thread. If you cut the thread undersize, you can possibly screw it in further, but it would not have much mechanical strength.
Warner & Swasey used to make a Chucking machine type of lathe for second operations, which had a provision to put thread rolls on it to act as a lead screw. Something like that would be “perfect”. The reason I am inquiring is that I want to make some High Pressure vessels for air guns to mate up with existing parts. I have the parts on hand to make a hydrostatic testing tool. Just don’t want to take anybody out.
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its been rumored these are purely metric lathes guesstimates for imperial on the placard.
https://www.ebay.com/itm/8x16-Mini-Metal-Lathe-Automatic-Variable-Speed-DC-Motor-750W-1HP-Metalworking/264467115634?epid=3023718196&hash=item3d9377ee72:g:dtIAAOSwznZdkX79 (https://www.ebay.com/itm/8x16-Mini-Metal-Lathe-Automatic-Variable-Speed-DC-Motor-750W-1HP-Metalworking/264467115634?epid=3023718196&hash=item3d9377ee72:g:dtIAAOSwznZdkX79)
i have no proof of that as fining specs on the leadscrew etc are not somthing i looked into personally.some forum members own them,., big spindle bore 1.5 inches ( 38mm
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Thanks for all of the replies and the link. Gives me some more to think about while I digest this.
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Finally got around to checking out the specifics on Metric Transposing Gears for one of my lathes. I had thought that the cumulative error listed was per thread. Turns out, the total error is only .0026” per foot of lead screw traveled. That is very acceptable. I ordered a 63 / 80 gear set for my SB9. Says I will be able to cut .2, .25, .35, .4, .45, .5, .7, .8, 1, 1.25, 1.5, 1.75, 2, 2.5, 3, 3.5, 4, 5 mm pitches. That should work for most every thing that I need. Guess I was too spoiled by CNC Machines where you just plug the desired thread pitch into a canned cycle and go. Thanks again for the replies. Keith
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That eBay lathe looks interesting, but they should hire someone to rewrite the description and captions on the picture to standard lathe terms.
Hoping to set up a small space this summer, have a micro mill already, need a small lathe, and need a good 3d printer (probably a resin printer at this point).
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Keith, I just came across the thread so here is my input. I had the same problem a few years ago and ended up converting my 10x22 lathe to a ELS (Electronic lead screw)
for short money by purchasing a kit. It worked great but got me spoiled and ended up converting it to full CNC. I then installed the ELS on a HF 7x10 mini lathe which is my go-to lathe for small AG parts. I like the Z axis fine control, of the ELS, for turning and threading.
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Keith, I just came across the thread so here is my input. I had the same problem a few years ago and ended up converting my 10x22 lathe to a ELS (Electronic lead screw)
for short money by purchasing a kit. It worked great but got me spoiled and ended up converting it to full CNC. I then installed the ELS on a HF 7x10 mini lathe which is my go-to lathe for small AG parts. I like the Z axis fine control, of the ELS, for turning and threading.
Bob,
Thanks for the input. I have two SB’s, a Sheldon, and a flat-belt Hamilton. Just getting the transposing gears fit up on a SB. 3D printed gears, oversized bushing, excessive run-out perpendicular to the bore. Just proving it out with these gears. Then I will make my own for a couple of other lathes. May make the other SB into a CNC someday. I used to run CNC’s as my line of profession 30 years ago, along with everything else. I am supposed to be a mechanic, but I end up reworking / upgrading more things than replacing mainly due to the lack of affordable quality parts.
Thanks again, Keith
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Update for those who would like to know.
Metric Transposing Gears on SB9
Using 63 / 80 tooth transposing gears, (a ratio of .7875),in place of the 80 tooth gear on SB9 lathe to cut 1.5mm thread pitch, using the 13 TPI setting on the QCGB, gives a lead or screw pitch of .060576 inch, crest to crest. 1.5mm is .059062 inch. .060576 minus .059062 equals .001514 inch difference between desired and obtained screw pitch. So, for every thread cut, you gain .0015 inch. After cutting 10 threads at 1.5mm, the lead is off by .0151 inch for .605 length of thread. Not so good.
I found that I could substitute the Reverse Lever 20 tooth Stud Gear with a 26 tooth gear, with the QCGB set at 22 TPI, to obtain a lead of .05909 inch which is not to bad.
I have not had the time to do the math to figure all of the combinations. I just need to cut a 40mm length without a lot of cumulative error.
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Hi Keith, Are you sure the error would be cumulative? The distance between the threads should stay the same, regardless of the length of the thread. HTH
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Hi Keith, Are you sure the error would be cumulative? The distance between the threads should stay the same, regardless of the length of the thread. HTH
Valid point. Thanks! Checking with my pitch gauge, it looks to be cumulative, (1+1+1=3; 1.5+1.5+1.5=4.5 for a total gain of 1.5 from origin). I will put the travel dial on it and check. The stacked length appears to get greater as the thread length increases.
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James is spot on , otherwise , youd have variable pitch on a manual machine which until now has only been accompllished on cnc
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James is spot on , otherwise , youd have variable pitch on a manual machine which until now has only been accompllished on cnc
I still am having trouble understanding.
1.5mm = .0590625 inch
With Transposing Gears for 1.5mm = .060576 inch
10 x .0590625 = .590625
10 x .060576 = .60576
.60576 - .590625 = .015135 difference from start
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You could always turn 10 revolutions and check with calipers, 50 turns would be better but now you are sacrificing a lot of stock.
Just a scratch pass should be enough to measure and see what the result is going to be.
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You could always turn 10 revolutions and check with calipers, 50 turns would be better but now you are sacrificing a lot of stock.
Just a scratch pass should be enough to measure and see what the result is going to be.
Scratch pass is what I did that showed the error. Funny, how CNC machines have lead screw compensation features built in.
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James is spot on , otherwise , youd have variable pitch on a manual machine which until now has only been accompllished on cnc
I still am having trouble understanding.
1.5mm = .0590625 inch
With Transposing Gears for 1.5mm = .060576 inch
10 x .0590625 = .590625
10 x .060576 = .60576
.60576 - .590625 = .015135 difference from start
yes i get that.. what im describing is thread crest to thread crest should never change.. yes, it may be a longer section ( or shorter ) to hit 20 crests, but the threads should be uniform to each other as the leadscrew is always spinning the same rpm as when the threads started.
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James is spot on , otherwise , youd have variable pitch on a manual machine which until now has only been accompllished on cnc
I still am having trouble understanding.
1.5mm = .0590625 inch
With Transposing Gears for 1.5mm = .060576 inch
10 x .0590625 = .590625
10 x .060576 = .60576
.60576 - .590625 = .015135 difference from start
yes i get that.. what im describing is thread crest to thread crest should never change.. yes, it may be a longer section ( or shorter ) to hit 20 crests, but the threads should be uniform to each other as the leadscrew is always spinning the same rpm as when the threads started.
I posted this so that others would know what to expect out of the 63/80 gear set. OK for a couple of threads, but that is about it. If / when I find something better, I will post. Thanks again for the replies.
Keith
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Can you buy a metric lead screw, or is that too much work to swap? Since I don't own one, I'm not sure of the process or if you can even get a different lead screw.
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Another thing to consider is that you will probably cut a 75% thread, which will leave some free play in the thread, which should be able to accommodate a thread pitch that isn't exact.
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If you have room and can find one; a 127 tooth gear will give you a true metric thread; since it is the lowest even multiple of the 2.54 cm/in or 25.4 mm/in conversion....
Here's a link to where someone else explained it rather well; and I stole my info from ;D
https://bbs.homeshopmachinist.net/forum/general/38898-metric-threading-with-120t-127t-gears (https://bbs.homeshopmachinist.net/forum/general/38898-metric-threading-with-120t-127t-gears)
Jesse
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If you have room and can find one; a 127 tooth gear will give you a true metric thread; since it is the lowest even multiple of the 2.54 cm/in or 25.4 mm/in conversion....
Here's a link to where someone else explained it rather well; and I stole my info from ;D
https://bbs.homeshopmachinist.net/forum/general/38898-metric-threading-with-120t-127t-gears (https://bbs.homeshopmachinist.net/forum/general/38898-metric-threading-with-120t-127t-gears)
Jesse
Thanks for the suggestion! This had been addressed elsewheres time and time again. Just not a whole lot of relevant data, ( a lot of supposition). The 80 / 63 gear set is basically the same ratio as the 127 / 100 gear set. There are other required gears that Have to be used with them. I was able to cut my M27 x 1.5 x 40 thread using a 26 tooth stud gear, (that I made), in place of the standard 20 tooth stud gear with very little error. I have not found a positive link to the gear and QCGB combinations. Just a lot of, “These work”. Well, there are other parts of the equation that are required. The most positive setup data that I have found relates to Lathes with change gears only. I may just make the gears for my older SB9 Workshop model lathe, and have that as my designated “Metric Lathe”.
Thanks again for the replies. When I get some good data on the required setups, I will post it.
Keith
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This is the complete set with a chart for South Bend 9A and 10K lathe with Quick Change Gear Box.
https://www.ebay.com.au/itm/124387115378 (https://www.ebay.com.au/itm/124387115378)