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Fixed my lathe and cut my first optical threads! :)

ATM DIY
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#1 kw6562

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Posted 30 December 2019 - 09:01 PM

Several years ago I bought a used Enco lathe but the gearing was not setup properly (I'm not sure what the previous owner was trying to do) and I didn't need to cut threads for most of what I have been doing since, so during holiday vacation I decided to fix it then learn how to cut threads.  After making the repairs (mostly adjusting gear positions on the shafts, adding grease, and replacing the disposable nylon safety gear with a metal gear) I spent some time watching videos and reading about various tricks and techniques.  One video from YouTube showed a way to cut threads in reverse - that is, with the feed starting at the relief and moving away from the work so that it is easier to stop.  I thought I'd try that - the tool is held inverted in the holder (for my setup I made a piece to hold the tool at the correct height) and the motor is run in reverse.  The gearing was set for a 0.75mm pitch and I used a standard 60 degree tool.  After turning a piece of stock to 48mm diameter I cut the thread in three passes to a depth of .020" (if I'm correct the depth should be .018" but I went a little over) then bored the piece and cut it off to make a 2" barrel coupler (I know they are available at Surplus Shed, and I have some, but I thought this would be a good starting project).  After a little clean up I tried it and was pleasantly surprised at how easily it threaded into a barrel from either end!  So I would like to hear from some of you experienced machinists out there - was this a stupid idea, should I have done it conventionally?  I found very little information on cutting optical threads - any suggestions?  Thanks for reading and clear skies --Keith

 

m48_thread.jpg


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#2 RichA

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Posted 30 December 2019 - 09:30 PM

Emco.  The threads look like they have a bit of "periodic error."  Would that be due to the cutter tip or the lathe itself?  This would be a great facility to have. A lot of those crappy Chinese lathes being sold by various hardware chains don't offer it.


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#3 mark77

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Posted 30 December 2019 - 09:33 PM

The upside tool in reverse is a very common way to do threads.  Also, depending on your cross feed travel, you can put the tool on the back side and run in reverse.  I have used an internal threading tool to do this if I didnt have enough travel to get an entire tool on the back side.

 

The key for optical threads is that they are SMALL.  Very sharp points on the bits, I prefer carbide threading inserts. 

 

Looks like a great start.


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#4 evan9162

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Posted 30 December 2019 - 10:07 PM

My only concern with cutting "up" is that lathes are usually designed only for downward pressure on the tool, tool holder, compound, cross slide, and carriage.  There may be some additional flex or play when the tool is pulled up vs. when it's pushed down.

 

I like to clean up my threads by doing a final pass without advancing the compound.  I usually end up taking off another thousandth due to flex in the previous pass - and the final cut ends up very smooth.  I also use cutting compound to smooth out the cuts.


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#5 kw6562

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Posted 30 December 2019 - 10:54 PM

Emco.  The threads look like they have a bit of "periodic error."  Would that be due to the cutter tip or the lathe itself?  This would be a great facility to have. A lot of those crappy Chinese lathes being sold by various hardware chains don't offer it.

Actually it is Enco, which is a crappy import that is similar to Grizzly, Harbor Freight, etc.  (I wish it was an EMCO grin.gif...) I was trying to understand how you noticed the error then I looked at the reflection in the photo which shows variations from the thread to thread, but I think that's mostly due to the roughness of the cut.

 

My only concern with cutting "up" is that lathes are usually designed only for downward pressure on the tool, tool holder, compound, cross slide, and carriage.  There may be some additional flex or play when the tool is pulled up vs. when it's pushed down.

 

I like to clean up my threads by doing a final pass without advancing the compound.  I usually end up taking off another thousandth due to flex in the previous pass - and the final cut ends up very smooth.  I also use cutting compound to smooth out the cuts.

Thanks, that's a great suggestion regarding the final pass and using compound to clean it up.  The compound definitely helps ---

 

finethread2.jpg

 

Need a lot more practice!  --Keith


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#6 dmcnally

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Posted 30 December 2019 - 11:10 PM

Hi kw6562,

I'm glad you're having fun with the lathe.  I will point out a potential safety issue.  You should only run the lathe backwards if you have a cam lock chuck.  If you have a threaded chuck the reverse spin will unscrew the chuck and it can come flying off the spindle and do all kinds of nasty things to you or the surrounding area.

 

Have a Happy, and safe, New Year.

Dave


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#7 don clement

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Posted 31 December 2019 - 01:34 AM

 So I would like to hear from some of you experienced machinists out there - was this a stupid idea, should I have done it conventionally?  I found very little information on cutting optical threads - any suggestions?  Thanks for reading and clear skies --Keith

IMO using the reverse helix method was the right way to cut RH threads up from a blind shoulder. I have done this many times on my Chidotcom 12x36 lathe with excellent results. I had a cam lock chuck so threading with the spindle running CW didn't pose a issue for me. If I had a threaded spindle then making a split-clamp on the threaded spindle would be my next project so I could cut threads with the spindle running CW. A couple of observations: First I don't think you made enough passes using only three. I would take more passes with less depth of cut. Second the real advantage of threading in reverse and feed towards the tailstock is that you can get the surface speed up and not have to worry about running into the blind shoulder. I know for me using carbide insert full topping tool that is really an issue but for HHS tool it is important also. Nowadays running high surface speed threading on aluminum I get excellent results with no cleanup needed. Also I use Relton A9 as a cutting fluid with aluminum. I am not a real machinist so take what you like and leave the rest.

 

Don

 

Reverse helix threading with tool upside down.

 

reverse-helix-external_zpsc0d0ff86.jpg


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#8 TSSClay

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Posted 31 December 2019 - 04:28 AM

Your threads look good, especially for a first try. Typically you would feed the thread a small amount at a time using the cross slide set to 30 degrees. The main dial for the axis would be returned to 0 for each cut. This let's you cut with one side of the cutting tool.

In order to get to the shoulder you can make a relief undercut just slightly deeper and wider than the thread. Use small cuts on each pass and use something (WD 40 works well) to lubricate the cuts.

Threading is a great skill to have!

Clay
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#9 windowpane

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Posted 31 December 2019 - 06:31 AM

Your threads look good, especially for a first try. Typically you would feed the thread a small amount at a time using the cross slide set to 30 degrees. The main dial for the axis would be returned to 0 for each cut. This let's you cut with one side of the cutting tool.

In order to get to the shoulder you can make a relief undercut just slightly deeper and wider than the thread. Use small cuts on each pass and use something (WD 40 works well) to lubricate the cuts.

Threading is a great skill to have!

Clay

When I looked closely at those threads I wondered about the cross slide setting- they look as if they may have been cut with the tool at 90, but that might be my eyes/photo artifact.


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#10 evan9162

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Posted 31 December 2019 - 09:31 AM

When I looked closely at those threads I wondered about the cross slide setting- they look as if they may have been cut with the tool at 90, but that might be my eyes/photo artifact.

It's not just you.  Those look like some of the first threads I ever cut, just using the main cross slide, instead of advancing the compound at 30*.  


Edited by evan9162, 31 December 2019 - 09:31 AM.

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#11 PETER DREW

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Posted 31 December 2019 - 09:51 AM

A good start I would say. The "chatter" appearance on the finish is probably a combination of too heavy a cut and lack of rigidity of the lathe. Try finer finishing cuts, for a very clean finish I use lubricant and turning the chuck slowly by hand with the lead screw engaged for the final cut. 60 years turning experience.
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#12 windowpane

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Posted 31 December 2019 - 09:53 AM

It's not just you.  Those look like some of the first threads I ever cut, just using the main cross slide, instead of advancing the compound at 30*.  

Ha! That is exactly what I was thinking!  I was really puzzled until I figured out what I was doing wrong.


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#13 SkyRanger

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Posted 31 December 2019 - 09:56 AM

Glad you didn’t cut off your finger which is what I thought when I first saw the title!

GG
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#14 PrestonE

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Posted 31 December 2019 - 09:58 AM

I cut all of our threads with the tool upside down and cutting from 

the head stock to the tail stock...

 

So much safer and threading puts a very light load on the system...thus,

never a problem...

 

Learned this from Joe Pieczynski on his YouTube channel...

 

Never again thread toward the Headstock unless it were a thread

that had a flange on the right side and needed threads going away

from it toward the Headstock...

 

Best Regards,

 

Preston


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#15 MKV

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Posted 31 December 2019 - 10:57 AM

I always cut threads at a compound angle of 29.5 degrees. It's like cutting butter. There's no rubbing or chatter.

 

Other than the compound angle, a freshly sharpened tool at 60 degrees is a must in my book. One can make suitable jigs for both grinding and setting the compound. Jigs make the setups quicker, easier and consistent.

 

Plunging a tool at 90 degrees to cut threads will work for very fine and shallow threads where the amount of rubbing and chatter is minimal.

 

Use generous amount of cutting oil. When possible

 

For short threads I prefer manually turning the lead screw with a hand crank. Just make sure you never reverse it before puling back the tool.


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#16 kw6562

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Posted 31 December 2019 - 01:06 PM

Great advice guys, thank you so much!  And good eyes - yes, I did use the cross slide with the tool at 90° - I thought for a shallow cut that I could get away with that.  Will definitely set the compound to about 30° and try feeding that way.

 

IMO using the reverse helix method was the right way to cut RH threads up from a blind shoulder. I have done this many times on my Chidotcom 12x36 lathe with excellent results. I had a cam lock chuck so threading with the spindle running CW didn't pose a issue for me. If I had a threaded spindle then making a split-clamp on the threaded spindle would be my next project so I could cut threads with the spindle running CW. A couple of observations: First I don't think you made enough passes using only three. I would take more passes with less depth of cut. Second the real advantage of threading in reverse and feed towards the tailstock is that you can get the surface speed up and not have to worry about running into the blind shoulder. I know for me using carbide insert full topping tool that is really an issue but for HHS tool it is important also. Nowadays running high surface speed threading on aluminum I get excellent results with no cleanup needed. Also I use Relton A9 as a cutting fluid with aluminum. I am not a real machinist so take what you like and leave the rest.

 

Don

 

Reverse helix threading with tool upside down.

 

attachicon.gifreverse-helix-external_zpsc0d0ff86.jpg

Don, what do you mean about making a split clamp for a threaded spindle? As Dave mentioned I should take precautions to prevent the chuck from spinning off when cutting in reverse.  There is a little bracket with a screw on the chuck that engages a relief on the spindle to help keep the chuck locked in place but I wouldn't want to rely on it now that this possibility has been pointed out to me; on the other hand I'm only taking light cuts in aluminum. I'd feel better with something more robust.

--Keith



#17 dmcnally

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Posted 31 December 2019 - 01:36 PM

Don, what do you mean about making a split clamp for a threaded spindle? As Dave mentioned I should take precautions to prevent the chuck from spinning off when cutting in reverse.  There is a little bracket with a screw on the chuck that engages a relief on the spindle to help keep the chuck locked in place but I wouldn't want to rely on it now that this possibility has been pointed out to me; on the other hand I'm only taking light cuts in aluminum. I'd feel better with something more robust.

--Keith

Hi Keith,

I asked Don the same quesion in a PM.  He pointed me to a post on Practical Machinist.

 

Here's the first link: click here.

 

Here's the second link: click here.

 

This didn't work for my lathe, but it might work for yours.

 

Happy New Year,

Dave


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#18 don clement

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Posted 31 December 2019 - 01:51 PM

 

Don, what do you mean about making a split clamp for a threaded spindle? As Dave mentioned I should take precautions to prevent the chuck from spinning off when cutting in reverse.  There is a little bracket with a screw on the chuck that engages a relief on the spindle to help keep the chuck locked in place but I wouldn't want to rely on it now that this possibility has been pointed out to me; on the other hand I'm only taking light cuts in aluminum. I'd feel better with something more robust.

--Keith

Also in addition to what Dave said this guy had some good videos on how he fixed the threaded spindle running in reverse. https://www.youtube....h?v=unlEQsB1LfE

https://www.youtube....h?v=hv2UyFNZUEY

 

Don

 

BTW I get excellent results threading using only the crosslide for thread pitches finer than or equal to 16tpi. The trick for me in getting excellent surface finish when threading aluminum with no deburring necessary is to use the highest spindle speed (surface speed) that the threading tool can handle.  e.g 500 rpm sometimes with carbide insert tools and smaller diameters. For me that means running the spindle in reverse (CW) and feed toward the tailstock for internal and external RH threads. Also I use Relton A9 cutting fluid when threading aluminum.

 

Reverse helix threading a RH internal thread. Note for internal threads the tool is upright on the inside rear part wall

 

AP2_7Adapter_3593_zpszw9vjfdj.jpg


Edited by don clement, 31 December 2019 - 04:34 PM.

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#19 kw6562

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Posted 31 December 2019 - 05:11 PM

Also in addition to what Dave said this guy had some good videos on how he fixed the threaded spindle running in reverse. https://www.youtube....h?v=unlEQsB1LfE

https://www.youtube....h?v=hv2UyFNZUEY

 

Don

I liked those videos a lot, thanks.  I'll probably do something similar.  For now, I drilled a recess in the spindle and drilled and tapped a hole in the chuck face plate boss for a 1/4"-20 set screw.  That plus the existing bracket should be okay; but I will make a split ring clamp in the near future.  Again, thanks for your help and advice.  --Keith

 

spindle.jpg

spindle_lock.jpg


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#20 gregj888

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Posted 31 December 2019 - 05:39 PM

29.5 degrees.  I have an old atlas with change gears (as in a stack of gears you change).  For metric, I can't use the dial as the gearing doesn't come out even so have to do both front and back by hand without disengaging. No issue of running into the the work piece.  Very light cuts, carbide and A9 for lube...


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#21 ATM57

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Posted 02 January 2020 - 05:11 PM

 I am not a real machinist so take what you like and leave the rest.

 

Don

I've seen some of your work... I would classify you as a machinist cool.gif waytogo.gif 


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#22 don clement

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Posted 07 January 2020 - 01:28 AM

I might add that on my Graziano SAG 12 spindle speed control is by switching in or out six electromagnetic clutches by twisting a joystick  so spindle speed changes can be made on the fly while the spindle is running. Also forward and reverse spindle changes by raising and lowering the joystick. In the middle position of the joystick the spindle is in neutral. The spindle will stop with in a 1/4 revolution by shifting the joystick to neutral and pushing the button on the end of the joystick. This feature also dictates the use of a cam lock spindle. This is great feature for conventional threading with the spindle running CCW and feed towards the headstock. That said, I still prefer the reverse helix method of threading with spindle running CW and feed towards the tailstock for both internal and external RH threads.

 

Don

 

The joystick control with instantaneous stop button is shown at the rear in this photo just under the Advent sign (yeah the Graziano really likes Pink Floyd when when turning Meddle). Also I built the knurled knob on the cross-slide handle as it was missing. Original similar knurled knob shown below on the carriage handle.

 

SAG12Knob_0626_zpszpmugbyg.jpg

 

 

BTW I was too cheap to buy a VFD to generate 3 phase from my single phase house AC supply and  control the 3hp 3ph motor (Thank you Nikola Tesla) so I cobbled  and built up a rotating 3 ph converter using a $5 5hp 3ph motor, a couple of contactors, and added a few capacitors used to balance the two generated phases. Low tech but works really well.


Edited by don clement, 07 January 2020 - 05:05 PM.

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#23 kyle528

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Posted 07 January 2020 - 12:12 PM

Feeding your tool with the compound (29.5 degrees or somewhere close) causes the tool to only cut on the left hand side, halving your contact with the work. Feeding with the cross slide will engage both sides of the tool. I wouldn’t work in reverse if your lathe has a threaded spindle nose, something to check. Threading in reverse can work well, but you must ensure the gibs are tight in all axes, or the work will try to lift the entire carriage upward, causing chatter. With some practice, cutting toward the head is no problem, once you’re used to being quick with the half nuts.


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#24 evan9162

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Posted 07 January 2020 - 01:38 PM

You cannot disengage the half-nut on many lathes when you are cutting metric threads (the threading gauge is useless for metric).  If you do, you have to re-index for the next pass.

 

On my lathe (a '70s vintage Atlas 6x18) the spindle can be disengaged from the main pulleys (while still being engaged to the lead screw) so it freewheels.  Then the back gear lever can be flipped up to engage low speed mode.  At the lowest speed, it turns at around 50 rpm.  I do my threading with this setup (low speed, with back gears)

I cut threads towards the spindle.  I first cut a relief on the spindle side of the threads (ending side), then start a cutting pass. 

 

Once the tool gets into the relief, I flip the back gear lever down, which stops everything almost immediately (the motor continues to run, disengaged from the spindle).  It's safe to disengage the back gears under load like that (though definitely not safe to engage them when the motor is running)

 

Then I turn off the motor, back away the cutting tool, and manually "rewind" the whole thing by turning the spindle backward by hand.  Once the tool clears the piece, I zero out the cross-slide back to the starting position, advance the compound, push the carriage against the lead screw to take up any backlash, flip the back-gear lever back up, and turn on the motor again for another pass.  

 

Lather, rinse, repeat.

 

By keeping the half-nut engaged and rewinding everything by hand, everything stays aligned and indexed to the threads.  I even do this with inch threads, since I haven't been successful engaging the half-nut based on the thread indicator.


Edited by evan9162, 07 January 2020 - 01:38 PM.

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#25 don clement

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Posted 07 January 2020 - 01:58 PM

Threading in reverse can work well, but you must ensure the gibs are tight in all axes, or the work will try to lift the entire carriage upward, causing chatter. With some practice, cutting toward the head is no problem, once you’re used to being quick with the half nuts.


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 I get excellent results threading in reverse  with great surface finish and no cleanup required. I use laydown carbide inserts so must have high surface speed (e.g. spindle running at 500 rpm) to get those excellent results when threading. I have very good hand eye coordination but not good enough to open the half-nut before crashing when threading  with feed towards the headstock at 500 rpm for realistic thread pitches. Threading in reverse with feed towards the tailstock  there is no problem with  crashing opening the half-nut @ 500 rpm. Of course my lathe has an inch pitch leadscrew and I don't use the half-nut at all when threading metric threads so even worse to stop before crashing when threading up to a blind shoulder. I like threading in reverse and never have to feed by hand.

 

Don


Edited by don clement, 07 January 2020 - 01:59 PM.

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