An ELS procedural question

[homebrewed]

This question was prompted by a project to replace my 7x12's top slide with a much more rigid riser block. I had resigned myself to needing to swap it out with the top slide when I was doing a single-point threading job, but a recent build thread about the ELS got me thinking. What are the procedural details involved when cutting threads with an ELS?

Background: In all-manual threading the usual approach is to rotate the top slide so it is at a 29.5 degree angle relative to the cross slide, but there also is an approach which reproduces the 29.5 degree tool trajectory using orthogonal movements. In this scheme, the top slide is oriented so its motion is parallel to the long axis of the work (parallel to the carriage movement). To cut threads the cross slide is advanced "X" amount and the top slide is advanced by an amount equaling tan(29.5)*X, or .5658*X. The advantage of this method is that the cross slide directly indicates the thread depth.

So if the lead screw is decoupled from the spindle (in an ELS setup), it should be possible to just use the cross slide and ELS to cut threads using the above-mentioned method. Each threading pass would simply jog the LS by .5658*(cross slide displacement) prior to starting the cutting pass. No compound needed, so if I build an ELS I could, theoretically, permanently lose the top slide. Hence my question regarding the typical process used to cut threads on an ELS equipped machine.

 

[RJSakowski]

This question was prompted by a project to replace my 7x12's top slide with a much more rigid riser block. I had resigned myself to needing to swap it out with the top slide when I was doing a single-point threading job, but a recent build thread about the ELS got me thinking. What are the procedural details involved when cutting threads with an ELS?

Background: In all-manual threading the usual approach is to rotate the top slide so it is at a 29.5 degree angle relative to the cross slide, but there also is an approach which reproduces the 29.5 degree tool trajectory using orthogonal movements. In this scheme, the top slide is oriented so its motion is parallel to the long axis of the work (parallel to the carriage movement). To cut threads the cross slide is advanced "X" amount and the top slide is advanced by an amount equaling tan(29.5)*X, or .5658*X. The advantage of this method is that the cross slide directly indicates the thread depth.

So if the lead screw is decoupled from the spindle (in an ELS setup), it should be possible to just use the cross slide and ELS to cut threads using the above-mentioned method. Each threading pass would simply jog the LS by .5658*(cross slide displacement) prior to starting the cutting pass. No compound needed, so if I build an ELS I could, theoretically, permanently lose the top slide. Hence my question regarding the typical process used to cut threads on an ELS equipped machine.

I am in the final steps of building an ELS based on Clough42's design. I have only cut a few threads with it so far but the process t6hat I used is exactly the same as with the gear driven lead screw.

The Clough42 design doesn't track position. It only rotates the lead screw in direct ratio to the spindle rotation. In order to accomplish what you are trying to accomplish, you would need to manually inject additional steps in the pulse stream.

Offhand, I would think that it wouldn't be that difficult to do so. I can see that it would be possible in the controller software or that it would be possible to switch the output to a manual position and inject the pulses to jog the position. Either way, I would think that you would want an additional readout displaying position so you knew how far the lead screw hd been advanced since the amount of advancement would depend upon the depth of cut for each pass.

It sounds like you might be moving closer to a CNC lathe where all of that could be programed in via the G code.

 

[mksj]

You do not need to use the top slide, nor set it to 29.5 degrees if you are cutting a thread using a cross slide. You only need to manually advance the cross slide. The issue is that this requires a more rigid machine and the depth of cut is a bit less per path, but that depends on the machine rigidity, cutter and material. I only use the cross slide for threading, the position of the cutter tip along the long axis does not change as opposed to advancing the tool post slide. Using the tool post slide cuts the chip predominately on the forward edge, cross slide cuts on both sides, the latter works better on smaller lathes. CNC lathe have a number of different cutting algorithms and can do complex cutter movements.

Example of a solid tool post:

PM1340 Solid Tool Post for Dorian BXA QC

After some hours of use on the Best & Jacobs Full Custom Edition PM1340, I decided it was time to improve rigidity of the toolpost by implementing a solid tool mount as a substitution for the compound when I don't need the function of the compound for normal turning activity. In many ways...

www.hobby-machinist.com

 

[greenail]

if you put a stepper on your x axis you are 60% to having a CNC lathe. CNC is also lots of work and it really doesn't pay for most simple stuff.

if you put a stepper on your X you can essentially cut threads/tapers etc AND your thread cutting can be fully canned which allows you to skip all the thread dial timing and cranking in/out and crashing.... clough42's doesn't support this but there are others that do or you can do you own. The stepper should cost you ~30-50 bucks and the stepper driver could be as cheap as $15. If you plan to use it often then it is worth it. You also get nice fine control over your cut per revolution with an ELS assuming you buy a decent encoder. The Rocketronics looks pretty good. If you are up for a challenge the Russian "electric guitar" lead screw project has about 600 pages of forum posts you can read with google translate.

I went with an centroid acorn board on my 7x10 lathe but I will likely just do an ELS for my 8x16 lathe. If the esp32 port of grbl supports spindle sync (no reason this isn't possible) then i may convert it to grbl. Fire and forget threading is very very nice vs the crank and pray old way. I've even "hard threaded" spindle shanks without breaking an insert!

Good luck, lots of options.

 

[homebrewed]

Not too interested in CNC'ing my mini lathe---- just about everything I do is a one-off so taking the time to write g code in that situation isn't worth the effort. ELS is about as far as I want to go. It's a specific-enough application that g code isn't required, and can be done so it still is possible to operate the lathe manually.

These mini lathes aren't all that rigid so reproducing the 29.5 degree tool path is desirable. I've cut .75mm pitch threads with just moving the cross slide, but I was threading brass, not steel.

Thanks to all for the feedback!

 

[greenail]

Not too interested in CNC'ing my mini lathe---- just about everything I do is a one-off so taking the time to write g code in that situation isn't worth the effort. ELS is about as far as I want to go. It's a specific-enough application that g code isn't required, and can be done so it still is possible to operate the lathe manually.

These mini lathes aren't all that rigid so reproducing the 29.5 degree tool path is desirable. I've cut .75mm pitch threads with just moving the cross slide, but I was threading brass, not steel.

Thanks to all for the feedback!

the tool engagement should be configurable but I'm not sure how it is set for the different ELSs. Getting rid of the compound should greatly improve rigidity. Thrust bearing mod will make it even better, parting is a breeze since I did both of those updates.

 

[homebrewed]

Am I correct in assuming your thrust bearing mod was done on the cross slide?

 

[greenail]

yes, i'm running just cross slide and no compound.

i made a video about it here:

since I made this I haven't felt the need to add the ballscrew so it is working pretty good!

 

[TorontoBuilder]

This question was prompted by a project to replace my 7x12's top slide with a much more rigid riser block. I had resigned myself to needing to swap it out with the top slide when I was doing a single-point threading job, but a recent build thread about the ELS got me thinking. What are the procedural details involved when cutting threads with an ELS?

Background: In all-manual threading the usual approach is to rotate the top slide so it is at a 29.5 degree angle relative to the cross slide, but there also is an approach which reproduces the 29.5 degree tool trajectory using orthogonal movements. In this scheme, the top slide is oriented so its motion is parallel to the long axis of the work (parallel to the carriage movement). To cut threads the cross slide is advanced "X" amount and the top slide is advanced by an amount equaling tan(29.5)*X, or .5658*X. The advantage of this method is that the cross slide directly indicates the thread depth.

So if the lead screw is decoupled from the spindle (in an ELS setup), it should be possible to just use the cross slide and ELS to cut threads using the above-mentioned method. Each threading pass would simply jog the LS by .5658*(cross slide displacement) prior to starting the cutting pass. No compound needed, so if I build an ELS I could, theoretically, permanently lose the top slide. Hence my question regarding the typical process used to cut threads on an ELS equipped machine.

This is one of the best suggestions for the an advanced feature of an ELS on a mini lathe that has eliminated the compound in favour of a sold tool post. Of course the addition of this feature would require stepper or servo motors to precisely advance the carriage and cross slide. Most minds then conclude that the lathe then must be made to be a full blown cnc lathe to accomplish this task.

In my opinion this is because many people don't know what a servo lathe or smart lathe is, but that's because mini lathes are so small there is not enough real estate to mount stepper or servo motors with encoder hand wheels attached to allow manual inputs as per a normal lathe. I'm only aware of one ELS product that allows smart lathe features on a mini lathe yet still attempts to permit manual machining... however, rocketronics has gone the route of a encoder handwheel to facilitate this functionality and it is in no way intuitive for a manual machinist who is used to handwheels on the lathe.

IMO again trying to implement this upgrade is a waste on any machine less than 10x20 in size... luckily for me I just acquired a precision 11 1/4" x 20" lathe and I do very much intend to convert it to be a smart lathe with encoder hand wheel mounted to the apron and cross feed.

I'm going to be looking for more such great suggestions, just so I can provide the very detailed requirements to the coders.

 

[ttabbal]

I haven't used a mini, but my 11x27 isn't a "big" machine. I just don't use the compound to thread, particularly since building a riser block. It can help in some ways, and it might be more important than I know on a mini, but it's never caused a problem for me. I tried it both ways, and just decided it was more trouble than it was worth for me.