My experiences with an ELS lathe

[David SeniorParticipant @davidsenior29320]

As Electronic Lead Screw (ELS) systems seem to be getting coverage at the moment, I though I would share some thoughts I wrote for the Raglan forum.

I have the Rocketronics 2-axis system that I fitted to my Raglan 5” lathe a few months ago.

Basic turning is, as expected, straightforward. The system requires both axes to be zeroed at a specific position (usually the outer corner at the end of the bar). If I am starting with a piece of round bar in the chuck, I will usually position the tool tip just clear of the corner in both directions, zero the axes in the control, then face the end by a small amount (maybe 0.5mm) and zero the Z axis again at the cleaned-up face. Then, assuming the plan is to turn down the diameter for a specified distance, I will set the cut length on the control, set it to only remove a small amount off the diameter, then set it going. Once done, I will reset the X zero to where it finished, and measure the diameter (positioning the tool at the last cut and re-zeroing is very straightforward). I dial in the amount still to be removed (measured diameter minus final diameter) and set it off again. The system uses a strategy of taking cuts along the length to a position about 0.1mm from the intended shoulder, then, after the final cut, it moves that extra 0.1mm and reverses out to clean up the shoulder. It works very well. Once going you don’t have to do anything apart from maybe swarf management. If that is proving a problem, pressing the ‘pause’ button will stop the cutting when the tool is back at the start, and you can turn off the spindle, remove the bird’s nest, restart the spindle and press ‘pause’ again to restart the cycle.

Of course there is nothing here that can’t be done with the standard lathe – it’s just easier with this – and you can work to an accurate length, which is probably not so easy using the Raglan carriage trip bracket.

The same basic method works for boring as well.

Parting off is just the same as the standard lathe if you are using the power feed.

Screw cutting is probably the reason why most people are attracted to these systems. It is certainly very easy and effective. Just set the pitch, the length of thread, the total depth of cut, and the number of passes. You don’t need a run-out groove (though there is a routine for making a DIN standard one if required) as this will make it’s own – it stops at the same place every pass. You can thread close to a shoulder without a problem (though, when I first tried this, I was going to leave only 0.5mm clearance, then realised that I was using an infeed strategy that moved down the flank of the thread so would be moving closer to the shoulder for every cut! I decided a bigger clearance would be prudent). And it is all done without any rattling gears!

I have also discovered (maybe everyone else already knew it) that by starting with a turned diameter of the exact nominal size (eg 10.00mm for an M10 thread), and zeroing the (full profile) tip on that surface, you get a good fitting thread just by using the book depth of cut. I did an M10 thread on a stainless shaft this afternoon, and the fit was lovely after a couple of extra spring- passes.

Tapered threads are also possible but so far I have found no need for this.

Tapers – internal and external. These were of specific interest to me as I have removed the top-slide and replaced it with a solid tool post mounting block, so I am no-longer able to angle the top slide to get tapers. To me the machining strategy seems a little strange, but it certainly works. You can enter specific dimensions (length and diameter change) but I have found it better to use what they call the ‘cone ratio’. That way you can extend the tapered section just by changing 1 distance – useful if you are trial fitting a tapered plug into a body, for instance.

I should mention that this system will only offer to make tapers in a specific orientation – external tapers with the small end nearer the tailstock, and internal tapers with the big diameter nearer the tailstock. It is possible to do them the other way round by reversing the Z-axis direction in the set-up pages, but you do need to be careful doing that. The same is required for LH threads, if you are unable to machine with the spindle turning the other way (very unwise with a screw-on chuck!)

Cutting radii – internal and external. With the same proviso that it will only do them in certain orientations, these are also straightforward. The handbook explains the process. One thing that you can do is to make what are probably elliptical curves – basically by specifying a different distance for the 2 axes. I thought this was just a gimmick, but then I realised I could make bullet-ended dome nuts for a water pump impellor that I was making – very neat and easy.

Grooving – it offers grooving with radiused bottoms (useful for pipe-bending formers), plus standard vee belt grooves. I haven’t needed to use these properly yet – just a bit of playing.

So, do I like it? The simple answer is, yes, I think it is brilliant. But it does depend on your approach to this hobby. I like tools to be ready to go with minimal set-up (hence my Multifix quick change tool post with a drawer full of holders and a wide assortment of screw-on tip tools). I like to plan the work. I am not so keen on doing it! I tend to make things from solid blocks, rather than castings, hence I have the attitude that if I make a mistake it is no big deal to start again. Also, machining from the solid tends to require more material to be removed, so being able to stand and watch is far more attractive than endless handle winding. A few days ago I had some 4” round aluminium billets that I had to reduce to 50mm diameter for a distance of about 40mm. I was only taking about 0.5mm radial depth of cut, so there were over 50 passes. I probably wouldn’t have volunteered to do the job without the ELS!

I do like the lack of noise. I hated the rattling of the gears on the standard lathe – I always disengaged them if I wasn’t using the power feeds or threading.

What don’t I like about it? Thankfully not much yet. It slightly niggles me that the readouts rarely give a round figure – if you want say 24mm it might say 23.999mm. Clearly no problem in terms of accuracy, but you do have to be careful not to read that as 23mm. I guess this is something to do with stepper motor resolutions and imperial lead screw pitches – it may not be possible to have the exact figure.

It would be nice to have a wider range of radius options. You only get a full 90 degree arc. I would prefer to be able to specify start and end angles to blend in to a taper, for instance. I asked about that with the makers but apparently the computing limit of the controller has been reached so there will be no major changes.

I have on a couple of occasions mistakenly caught the cross slide handle when the machine has been running, which has presumably over-ridden the stepper motor and lost the position. It’s a nuisance because you have to start again. Having done it more than once I decided to replace the handle with a plain disc to allow me to move the slide when required but hopefully with less chance of me catching it by mistake.

And of course there is the fear factor! Have I set it correctly? That is probably why I don’t use my mill in CNC mode. You don’t always get chance to stop it before something crashes if you have got it wrong! Thankfully this ELS doesn’t seem to have too many vices. The main thing to check is that you have got the axes zeroed in the correct position before you start a new cycle.

I should point out that I am not trying to recommend this system over any other – I haven’t seen or used any other. But if anyone else is thinking about this conversion I am happy to share my experiences. This (Rocketronics) system is expensive – I think it was about £1000 with all the motors etc. – and there are plenty of cheaper options available (though most are only powering the Z-axis so can’t do some of the functions available with the Rocketronics one).

I had always expected to use the ELS in conjunction with the DRO. The idea of having the DRO giving the overall position, and the ELS having it’s own local datums, seemed sensible. However, for this to be really successful I would need to have all the tools set in the DRO tool table. So far I have found the tool table function to be extremely counter-intuitive. I need to get my head around how to use it properly before it will be much use.

Dave

[DiogenesParticipant @diogenes]

Thanks for posting, Dave, some useful thoughts & comments there.

[JasonBModerator @jasonb]

Thanks David, having both axis under control opens up the possibilities a lot more than just the one.

[EmgeeParticipant @emgee]

Dave

To me that system sounds very much like a cnc set-up with limited functions.

How does it cope with feedscrew backlash ?

 

Emgee

 

[John HinkleyParticipant @johnhinkley26699]

If you want a comparable els like the Rocketronics one described by Dave, above, but not nearly so expensive, I highly recommend this product range. I have the single-axis version fitted to my mini lathe and it is excellent.  The videos of both versions make a fascinating watch whilst allowing you to brush up on your French – or switch on the translation sub-titles.

Emgee – the backlash issue is dealt with on the system I have highlighted by moving the tool beyond the “start” position before returning to that start and continuing with the cut. I would assume that the Rocketronics els behaves in a similar manner.

John

 

 

[David SeniorParticipant @davidsenior29320]

Emgee,

You’re right – it is a basic cnc conversion with limited functionality. The main difference is that you are using small individual actions, without them being added together. So you can’t, for instance, face an end and turn the diameter in one smooth motion – you have to do them as separate operations. It’s not a huge help for batch production – you still have to find the zero points for every section.

Backlash is manually measured and inputted to the software. Clearly minimal backlash is desirable, but the software makes allowance for whatever figure you have entered.

One point I didn’t make is that the lathe is still able to be used manually. With the threading half-nuts engaged you can’t use the Z-axis manually (though you could if you had a handle on the end of the lead screw), but releasing the half-nuts gives back manual control. Turning off the X-axis motor (by a button on the control panel) gives back manual control for the cross slide.

I can’t emphasise enough how the usefulness depends entirely on how you want to work, and what you enjoy doing and what you don’t. Clearly it won’t suit everyone, but so far I am absolutely delighted with it.

[BazyleParticipant @bazyle]

Re LH threads, and the opposite tapers. I think I an right in thinking that if you could intercept the stepper wiring with a multipole changeover switch you could reverse its direction without the ELS being any the wiser.

[David SeniorParticipant @davidsenior29320]

Bazyle

I’m sure you are right, and if it was going to be a frequent requirement then that would be simpler. It is not really a problem to go back into the settings pages and change the direction, but your way would give a visual indication of what was set.

Of course the ELS is none the wiser using the software to change the direction – it is effectively assuming you are setting it to use an opposite hand leadscrew. For threading it will still assume you are starting in fresh air beyond the end of the thread, and will make the normal allowances for acceleration distances etc. You just need to ensure you understand that it is going to plunge into the stock rather than air when it puts on the cut.

The manual (a proper printed book!) is good at explaining the tool paths, so if you change the directions you just need to ensure you understand what is going to happen.

 

[JasonBModerator @jasonb]

Only took me a moment to realise that I just need to move the carriage to the left using the ELS feed to take out any backlash before zeroing the tool and setting any distances and also to have the tool start a few mm from the end of the job

The twin axis is much like using the simple routines or “wizards” available for most CNCs where you may just want to face or cut a taper but don’t want to go through the CAD & CAM. Same as things like PCD and face on a CNC mill.

As I hinted in my other thread there are some quite reasonably priced complete single axis kits made for the far eastern machines. Not just the ELS but they include power supply, driver, stepper, encoder, belts, pullies and brackets and available for several models.

[Alan JacksonParticipant @alanjackson47790]

I wrote this and it appeared in the MEW a long time ago about my Stepperhead lathe and it is still valid.

Being able to engage/disengage or mix the axes to be operated by CNC or manually gives the lathe such a variety of operations all at the operators control. While it is old compared to modern standards TURBOCNC enables a very versatile range of operations all very adjustable and backlash is dealt with in the settings.

Alan

SECTION 5:  Stepperhead Operation Notes
I am still experimenting with Stepperhead but I can say that it works much better than I ever expected. I will go so far as to say it is fun to drive. It is surprisingly rigid compared to similar size lathes. I think headstock and spindle add much to this. I expected that the headstock being attached to the bed via the vertical column would be detrimental to the overall rigidity but I have not noticed it. Conversely one could argue that when the vertical column clamps are tightened it provides as rigid a mounting for the headstock as any conventional bolted arrangement. I have easily parted off 1” mild steel bar without any hint of distress or chatter and have purposely turned parts extended further from the chuck than is sensible with no hint of chatter. The saddle drive works very well, I can make a deep cut on manual or power feed and wind the tool slowly back without a fine additional cut being added due to spring (or saddle racking).

 

I am going to claim that this is due to the saddle drive leadscrew position moving the saddle without importing too much twisting moment although this is difficult to prove.

It is after all a test bed incorporating many untried and unconventional features and my first experience with CNC, stepper motors and electronic control. I have got used to the presence of the over arm, it does not seem to restrict or hinder operation. The gains in rigidity provided by the overarm being locked to the bed and headstock are quite palpable. The topslide can be moved anywhere on the cross slide.  Full use of this is realised when say turning a steep taper. The topslide can be positioned so that the cutting tool is past the centre of the component being made and the lathe run in reverse. This enables easy access to the top slide handwheel whereas normally the topslide will be positioned awkwardly close to the chuck. One is spoilt for choice here because this same operation can also be done with CNC control by setting the X and Y axes to move in unison to generate the same taper and at a controlled feed rate if required. Being able to control the mandrel speed and cutting feed during operation is also very convenient.  Deep cuts and fine feeds can be set to achieve a good finish.

 

The elevating mechanism seems to be able to do it’s lifting without too much effort. Subsequent dismantling showed that the rubbing surfaces of the worm and wheel were quite ok. The Z and X axes operate smoothly and give a good finish in manual mode and even better finish in manual controlled stepper drive.  There is not much need to change the belt position, the middle pulley size covers the speed range from 100 to 2200rpm, which is suitable for most operations, but screw cutting is best done on the biggest pulley at about 120 rpm because the additional torque keeps the speed more constant. The more constant the speed in screwcutting means that less acceleration/deceleration is demanded by the system to keep the thread pitch constant.

 

In some operations it seems advantageous to use a combination of CNC and manual inputs and this is a big plus for Stepperheads versatility.  For instance screw cutting using the computer to control the thread pitch and length and set the cut depth and withdraw manually. This is not full CNC, which can also be done, but perhaps, a model maker’s one off pragmatic version avoiding extensive programming and set up. This does not restrict full CNC in any way; it is just that it is an easy, useful option, which is only available due to the ability to mix manual and CNC operations.

 

CNC operates in either, ‘Absolute positioning’ which always starts from a preset zero position or ‘Incremental positioning’ which moves a set distance from the existing position with no reference to any home or zero position. Certain operations require either ABS or INC mode. For most of my operations INC seem preferable. It is very necessary to be sure that you are in the correct mode and failure to do so can give undesired and unexpected movements to the axes which can be quite disconcerting. I have set up for imperial units but metric can also be chosen.

 

In Turbo CNC there are two operating modes. The first is preset program control whereby the control instructions (G codes) are prewritten programs that can be recalled and used or copied and modified to suit the desired operation. The second mode is called MDI (Manual Data Input) whereby a single line of control code is keyed in and the instruction is then applied. This all soon becomes quite obvious but it must be carefully carried out. The machine will only do what you instruct it to do. Tell it to do wrong, it will.

 

As an illustration here is a simple example of incremental MDI mode. Tan 5 degrees = 0.0875. Type in G01 Z-1.000  X0.0875  F0.001  then press enter and it will move the saddle 1” towards the headstock and simultaneously move the cross slide 0.0875” away from the lathe centreline at a feed rate of 0,001”/rev. Which will machine a taper of 10 degrees. When the cut has finished change the input to G01 Z1.000  X-0.0875  F0.001 (Positives and negatives reversed) press return and the tool will move away from the chuck following the taper.  These figures can be varied at will to produce an infinite range of tapers (Morse 1, 2 etc) and feeds without having to carefully set the topslide at the angle required. I am certainly not an expert on CNC control. So I will avoid trying to teach a subject I am still learning. I just wanted to convey the advantages available to the home workshop.

 

I have found that using MDI mode with a manual override suits many of my requirements. What this means is, to machine the pre-described taper and be able to manually set the cut depth by using the topslide set at 90 degrees to the lathe axis permits a degree of manual control over pure CNC operation. The computer generates the taper and the amount to be removed is controlled by the operator.

 

Screwcutting is another operation, which becomes easier with computer interaction.

I use the word interaction purposely, because full CNC control requires careful and extensive set up to achieve the final result from a piece of bar stock to the finished item and if you are only going to produce one item it will consume a vast amount of precious time. Well it does for me. MDI mode will allow any screw pitch for a chosen length to be cut. By using the topslide set at say 27.5 degrees (for Whitworth thread angles) the thread depth cut can be set for each pass using the topslide. I set the speed at about 120 rpm (the screen gives a readout of the spindle speed).

 

The tool will then cut the screw thread to the length chosen and stop, finishing the thread with a cut depth undercut; because the tool stops moving but the mandrel continues rotating.  The tool is then manually withdrawn using the withdrawal lever on the topslide. This avoids the instant disengagement of the half nuts, before the tool hits a shoulder, which is necessary on a normal lathe and a genuine source of panic and fear.

 

To rewind the saddle for another cut the MDI input is modified by changing the Z-axis from minus to plus on the computer, hit return on the computer and the tool will return to the start position for a new pass. Reset the MDI Z axis back to minus, return the topslide withdrawal lever and set the new cut depth for the next pass then hit return again. Do this as many times as required until the thread is finished.  This may sound like an involved process but I am sure once observed it will seem a lot less complicated than the procedure on a manual lathe.

 

Left hand threads can be cut in the normal manner by starting the tool close to the headstock and moving away from the headstock with normal anti-clock rotation or by using clockwise rotation with the cutting tool on the far side of the lathe mandrel and moving the tool towards the headstock. The advantage of this is that it is not necessary to make an undercut to the thread depth to start the cut from.  Also CNC threading requires a small distance at the start of each cut to get synchronised with the lathe mandrel so an extra length needs to be added for this.  Any backlash in the drive is pre-compensated for in the computer setup. What I have described above has been my approach and findings so far and should not restrict or limit the use of the many other options possible, which are available with CNC control.

 

Photos 40 & 41 show what can be done. The lathe spindle was set at 5 degrees to the bed axis. I choose 13.5 TPI because you can. There is virtually no limit or restriction in the pitch selection. No need to select complex gear ratios between the mandrel and leadscrew as it is all easily dealt with by the computer. Just type in the desired pitch and thread length. This would be a challenging set up on a conventional lathe but simple with CNC and Stepperhead.

 

In full CNC mode the Z and X axes can be programmed to make simple to complex shapes repeatedly. Positive and negative curves etc I am still in the learning mode here. Once a program has been made for a particular component it can be saved and reused again. It can also be copied and modified to make a new similar program. So a library of programmes can be built up for future use.

 

One comforting aspect of a Manual/CNC mix is to be able to set up for a CNC based operation and dry run through the program with the cutting tool away from the material being cut. This can also be done on full CNC but the advantage is that when satisfied with the programmed operation, the tool can be gradually advanced to come into play with say the topslide handwheel. This gives a feeling of control over the electronic mindset rather than it doing what it wants without your permission. I am sure dedicated CNC people will laugh at this but it works for me.

[EmgeeParticipant @emgee]

Hi Alan

I don’t think anyone is going to laugh at you for being cautious and running the program “in air” to observe the movements are as intended, far better than having a crashed tool.

I run cnc lathes and find the Single block running feature useful for the same task, the program runs but only making a single line move until you press Run/Start again for the next line move.

If using such as Fusion360 you can simulate the cnc program compiled on screen, every cutting path is shown and runs through at your chosen speed.

Nearly all G code Editor programs have a similar feature so it is easy to check run a program before sending it to the machine.

Emgee

 

 

 

 

[DellParticipant @dell]

I also have Rocketronics on my Myford 10 mainly because I have trouble holding & turning a handle for any length of time & I am very happy overall but as David has said you have to make sure both axis are at zero ( don’t ask how I know ) as for backlash compensation there is a setting in the software setup also I think the system backs up further before the next cut, I have just made a taller tool rest for a Pultra 17/70 & I don’t think I could do that manually 

[David SeniorParticipant @davidsenior29320]

The zeroing of the axes before starting is the thing to be careful about – I also have learnt the hard way! Once you get into the habit it is not an issue.

[John HaineParticipant @johnhaine32865]

What it needs is an auto tool setter…

[DiogenesParticipant @diogenes]

2-axis system looks like it might offer some useful opportunities for forming cutters – with suitable ‘run-out’ room might even be possible to back them off?

[John HaineParticipant @johnhaine32865]

Here’s one I made earlier…  Profile is circular based on the “button” approximation for involute but could equally be a true involute or epicycloidal with a bit more maths.  Backing off possible in principle by moving the cutter in and out but in practice needs very fast synchronised radial movement which CNC controllers don’t support.  In this case the backing off was done by having 4 mounting positions for the blank on a fixture,

[DiogenesParticipant @diogenes]

👍😁

[Geoff RogersParticipant @geoffrogers81118]

Dave,

when fitting the Rocketronics kit, how did you cover the Estop aspect?

I am looking to fit the kit to my Myford  lathe.

 

thanks

Geoff rogers

[David SeniorParticipant @davidsenior29320]

Geoff,

If my memory serves me right, I just fitted an E-stop switch that had 2 pairs of contacts – one for the Rocketronics and one for the motor VFD, and found a convenient place to mount it.

Dave

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