Author Topic: Stepperhead 2  (Read 540 times)

Offline jackary

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Stepperhead 2
« on: March 15, 2021, 01:46:36 PM »
Stepperhead 2
What to do in the Covid lockdown? I wish you the best of health and hope you are coping with this trauma. In my case I have tried to deal with these long lockdowns by trying to design a smaller version of the Stepperhead lathe that I built and displayed in 2008 ( http://www.lathes.co.uk/stepperhead/ ).   I managed to get access to Solidworks and intended to teach myself in the process. You may have  seen that the Model Engineers Workshop magazine has recently published an article on this design. So this is a follow on from that and I am sticking my neck out here venturing for opinions from the forum members. I have added a few screenshots and a basic description.
I set myself a design brief as listed below:
1.   Size - A table top lathe suitable for the home workshop; or even indoors - with senior management approval of course! The machine is to be mounted on a baseboard of 750mm wide x 500mm deep. Of course the size can be easily increased, but a design for a limited footprint is more demanding in the use of the space.

2.   Concept – Mini lathe size - similar but smaller than the first Stepperhead design but with changes and improvements to simplify construction and operation.  A cast iron one-piece bed. The spindle drive motor and all the electrical components are housed in a box at the rear of the lathe which will also form the splashback or chip guard. The raising and lowering of the head, overarm and tailstock will be done by a vertical screw. similar to a milling machine table. This keeps everything above the base board.

3.   A Camlock spindle nose fitting. This is such a boon enabling easy chuck changes and the safe ability to rotate the spindle, under power, in either direction.

4.   The spindle motor is a 0.37 kW three phase motor, frame size 63, driven by an inverter also mounted in the splashback box. The motor is pivoted at its lower front so it can move as the head and tailstock is raised. This uses the motor weight to tension the belt. The motor & spindle pulleys have three steps for a wide speed range. The largest spindle pulley enables a low back gear speed range at the spindle. The belt is accessible and can be easily, and quickly, changed to the various pulleys. A polyvee belt drives either the spindle or a shorter length belt is used for an overhead drive shaft mounted in the upper section of the splashback box. The motor pivot point enables both drives to be adjustable. The pivot may benefit from some friction damping adjustment.

5.    The spindle runs on taper roller bearings and has a 26mm bore. The bore is as big as can be made without substantially increasing the head block size of 80mm square. It uses the same Camlock chuck mounting arrangements as Stepperhead. I tried to design a slightly smaller Camlock fitting but there was little to be gained with keeping the mandrel bore size and ER32 collet fitting.
The drive from the spindle stepper motor is via a worm wheel mounted on the spindle inside the head block. The stepper motor worm engagement is spring loaded when moved to into this wormwheel to drive the spindle. This gives a backlash free drive to the spindle. The worm drive is positively locked out when not required. This is to ensure that cannot be accidentally engaged. The motor belt can also be disconnected at the motor for additional safety. The stepper motor mounting box also incorporates an optical sensor and its circuit board for screwcutting etc.

6.   New ideas – I have incorporated some new features I have been experimenting with over the last few years. There are always reader comments about gibs and their settings for smooth shake free sliding. It is a fundamental requirement that dictates the performance of the whole machine. This requires accurate slideways and careful adjustment and is very difficult to achieve on less than perfect fits.

So here I would like to propose my oval gib idea to replace the conventional gib arrangements throughout. It seems to me such an improvement and simplification and has become subject to a patent application. It eliminates the adjustment and locking screws at intervals along the gib length. It contacts, solidly, both the sliding and fixed guideways the full length of the moving slideway. It is simply rotated to set the close sliding requirements by setting and locking an eccentric stop. If the gib is further rotated away from this stopped position it will lock the full length of the moving slideway solidly to the fixed slideway. Rotating it back to the stop will return it to the set close sliding position. It is also easy to make.

The oval gib itself can be solid or it can have a surface that is segmented into slightly springy zones. This will spread the loading and be of great assistance for smooth operation. It will also enable it to adapt to, and make the best of, less than perfect surfaces due to local wear or less than perfect machining. Of course it cannot compensate for non-parallel sliding surfaces and poor fitting, but it will tend to slightly deflect over the bumps and troughs, so to speak, and promote smooth shake free movement.  It is also easy to remove and replace for inspection and can be made from a variety of materials. The oval gib system has also been used to guide and lock the vertical column in the radial and vertical planes, avoiding the triangular gib which works well but was difficult to make.

7.   Tightening and undoing ER style collets seems to be a subject of contention, especially for the smaller diameters. So I have suggested a method of tightening the collet nut without having to lock the spindle, or use a second spanner to hold the chuck body. The castellated mandrel mounting body has fifteen notches and the nut has sixteen holes so there is always an appropriate zone for the locking/unlocking spanner. The collet nut has two hardened discs positioned to enable the collet to be withdrawn rather than an eccentric diameter.

8.   Vertical parting tool - I have shown a design which mounts on the front of the lathe and rests solidly on the cross slide, preventing any downward deflection and allowing free chip flow. Inserted tips could also be used in a suitable mounting. With the topslide locked by its oval gib it becomes a virtual Gibraltar mounting point because the upper and lower slides are locked together. The cutting tool height can easily be set even when the machine is in operation.

9.   The upper part of the splashback box provides a mounting for a horizontal secondary driveshaft in a similar manner to watchmaker and earlier instrument lathes. A cover panel at the centre of the splashback front panel can be either, slid to the left or just removed to reveal a rectangular cut out exposing this driveshaft with a pulley drive for round belts. The pulley is positioned along the shaft to provide the overhead drive. To fit the round belt, the shaft is moved to the left enabling the belt to be fitted over the end of the shaft. A locked collar retains the shaft in the righthand end bearing. The spindle drive belt is removed and a shorter length polyvee belt used to drive the shaft.

This makes use of the main motor with its inverter control, enabling a wide speed range for a milling spindle mounted on the topslide for example. The arrangement I used on Stepperhead with a milling head driven by a DC motor with electronic control worked but had a limited speed range around 2000 rpm. It had limited power and got quite hot, its bulk was also restrictive. The problem with the high speed was that a carefully shaped carbon steel cutting tool would overheat and lose its hardness halfway through the operation, say when cutting a gear, especially in steel. High speed steel cutters solve the problem but are difficult to make and shape compared to carbon steel. So to be able to slow down the cutting speed without power loss would be of great benefit.  Round belt pulleys and belts of various diameters can be used. This would enable a wide use of operations say, using the stepper driven spindle via manual or CNC control for a myriad of operations, including decorative ornamental designs etc.
 
10.    The milling spindle has a bore for No 2 Morse taper collets and a locking/eject drawbar. It has bronze self-lubricating bearings and uses a double taper similar to a watchmaker’s lathe headstock design. Ball bearings have been avoided to keep the overall diameter down to 40mm.
Comments welcome
Alan

 
 
 
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Offline vtsteam

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Re: Stepperhead 2
« Reply #1 on: March 15, 2021, 03:46:33 PM »
I really admired your original Stepperhead -- which was mentioned during my lathe build thread here on MM. Wonderful looking machine, and it's really nice that you've posted this new version here. Looks like there are some new innovative features in this one.

Do you think you will be building it, now that you've done the CAD design work?
I love it when a Plan B comes together!
Steve
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Offline MetalMagus

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Re: Stepperhead 2
« Reply #2 on: March 16, 2021, 08:20:04 AM »
That's really impressive.

Hope you build it and create a series in here for us to follow.

On the chuck, have you considered using 5C collets with a closer mechanism out the rear of the headstock for fast part change over. I know Taig have produced a 5C headstock, and have seen similar set ups on a Sherline lathe.

Regards

Sean

Offline vtsteam

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Re: Stepperhead 2
« Reply #3 on: March 16, 2021, 02:57:55 PM »
I see the new gib style on the lathe bed. I do have a question -- how do you scrape something like that into bearing? Would you need a special profiled straight-edge?
I love it when a Plan B comes together!
Steve
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Offline philf

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Re: Stepperhead 2
« Reply #4 on: March 16, 2021, 03:41:46 PM »
I'm confused about the 'oval' gib too.

Surely you can't ever practically have more than a line contact with an oval gib. If it was manufactured perfectly with the correct clearance built in then it would be feasible but as soon as you rotate the gib the curves won't fit resulting in line contact.

Or am I missing something?

Phil.
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Offline BillTodd

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Re: Stepperhead 2
« Reply #5 on: March 16, 2021, 04:48:55 PM »
I'm confused about the 'oval' gib too.

Surely you can't ever practically have more than a line contact with an oval gib. If it was manufactured perfectly with the correct clearance built in then it would be feasible but as soon as you rotate the gib the curves won't fit resulting in line contact.

Or am I missing something?

Phil.

I suspect a faux elipse/oval of two radii  with overlapping centres

Image a circle with section cut out across the diameter the squashed.
Bill

Offline jackary

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Re: Stepperhead 2
« Reply #6 on: March 17, 2021, 07:16:13 AM »
I wil endeavour to answer your questions about the oval gib.

The bed semi-circular groove is lower than the facing saddle semi-circular groove by a small amount creating an offset aperture between the fixed and sliding surfaces. The oval gib has a profile that closely matches but is slightly smaller than the aperture profile to permit insertion. The gib is rotated to set the sliding clearance and is then set in this position. Further rotation will lock the slides together.

The gib is anchored axially to the saddle but is free to contact both the fixed and sliding grooves. The gib urges the saddle to contact the bed flat top surface and the inner guideway surface in a manner very similar to a dovetail gib. The gib contact area will closely match the groove surfaces. I also have a design (not revealed here) that matches both grooves exactly, regardless of the offset distance.

The vertical column grooves would form a full circle when aligned but are purposely mis-aligned to form an offset aperture by the oversize first gib. A secondary gib is added below the first upper gib which can be rotated to urge the offset grooves into alignment, therefore locking the column in its slideway. The gib can have a simple oval profile or be more profiled to match the groove surfaces giving closely matching contact surfaces.

I do not think the grooves would be any more difficult to manufacture than a dovetail groove. The grooves have to be parallel, but to my mind there are no stringent machining requirements. Avoiding the adjusting and locking screws for a dovetail gib is a worthwhile simplification and avoids the point contact with the gib and the screw ends. To be able to lock the slideways over the full slideway length and return the gib for sliding contact is a bonus.

The gib makes full contact with both the sliding and fixed guideways. This makes it better at absorbing the machining forces and provides the benifit of a tapered gib without the precision requirements a tapered gib demands. I made a topslide featuring an oval gib for my Colchester Chipmaster lathe about 10 years ago and it works superbly.

Alan

Offline Muzzerboy

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Re: Stepperhead 2
« Reply #7 on: March 17, 2021, 09:37:11 AM »
It's difficult to understand how 2 concave cylindrical surfaces can be adjusted both vertically and horizontally relative to each other while both remain in full contact with the "cam" body. Clearly such a body needs to have 2 truly cylindrical convex surfaces with an offset ie not actually oval / elliptical.

The role of the conventional dovetail is to achieve vertical and horizontal constraint, which is why it is both simple and effective. It can also be machined with simple, straight edged tools. Wear and tolerances are taken up in a simple manner and this concept can use a wedge shaped gib rather than screws, to avoid point contacts.

I see you also have a design (not revealed here) that matches both grooves exactly, regardless of the offset distance. I'd be very interested to hear more - that is what these forums are about!

Offline jackary

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Re: Stepperhead 2
« Reply #8 on: March 17, 2021, 01:46:13 PM »
Hi Muzzerboy,
Your comment
(I see you also have a design (not revealed here) that matches both grooves exactly, regardless of the offset distance. I'd be very interested to hear more - that is what these forums are about!) means that I would be revealing what I have applied to patent without anybody signing a Non disclosure agreement. This would negate the patent claims etc before the patent is granted. So from my point of view it would not be a sensible thing to do.

Offline WeldingRod

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Re: Stepperhead 2
« Reply #9 on: March 17, 2021, 04:45:13 PM »
Now you've piqued my curiosty!  I'm guessing you are getting a low stress cylinder on closely fitted cylinder thing going here, rather than the attempted plane on (hopefully) parallel plane in a typical gib.

I saw you talked about the oval gib on PM back in 2013, but the pictures are dead (photo crud bucket).  Any chance of a link to the published application, assuming its past the 1 year publication time?  I can't find anything clearly yours on USPTO or Goog patent. If it hasn't published yet, no worries,  my curiosity can hold out that long ;-)

Ah, sorry!  UK patent.  No clue what your publishing stuff looks like!

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Offline vtsteam

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Re: Stepperhead 2
« Reply #10 on: March 17, 2021, 10:52:22 PM »
Thanks Jackary for explaining!  :beer:

re. "I do not think the grooves would be any more difficult to manufacture than a dovetail groove. The grooves have to be parallel, but to my mind there are no stringent machining requirements."

I guess you could say that for all lathe bearing surfaces of any sort. Or to put it another way, the precision of the lathe depends on the precision of the bearing surfaces, and stringency of machining (or scraping into bearing) is the measure of quality.

It isn't in the machining or scraping per se I was asking about, rather the means of checking it. Conventionally a straight edge is used on straight profiled lathe sections, but with a curved profile, do you anticipate using a curved profiled straightedge? And when these surfaces wear, as they do in all lathes, and unevenly, as they do generally towards the headstock end, how will this be corrected, even with a profiled straightedge to test, and what kind or shape of scraper?

I remember Mr. Urwick invented the triangular gib for a vertical sliding head on a round column, and your lathes have a clear relationship to his. He patented the triangular gib, but unfortunately it was never widely adopted. Round column Asian milling machines like the one I own would have been a logical beneficiary, but his ideas are largely unused. I hope you have better luck, and besides the desire to do something different, I also admire the beauty of your machines.
I love it when a Plan B comes together!
Steve
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Offline jackary

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Re: Stepperhead 2
« Reply #11 on: March 18, 2021, 07:25:16 AM »
Hi WeldingRod,
You are correct I did show my topslide with an oval gib but I think I avoided any detail description then. I have been musing over the idea since then and finally decided that it was worth patenting so the application has not yet been published. I think it will be some time before this happens it seems a long winded process. As to whether it is all worth while who knows. One thing for sure is as soon as you show something different the naysayers etc emerge. I will let you all know once it is published.
Screenshot shows a Lever Locking Topslide with an oval gib, lever below feed dial can be lifted to lock the slideways.
Alan
« Last Edit: March 18, 2021, 08:00:35 AM by jackary »

Offline jackary

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Re: Stepperhead 2
« Reply #12 on: March 18, 2021, 07:35:32 AM »
Hi vtsteam,
Thank you for your kind comments. As to checking a worn or inaccurate groove I think the procedure could be carried out using a close fitting circular rod and a dial guage referenced to the inner sliding surface of the bed. in a similar way to checking a dovetail groove. The gib can incorporate a degree of flexibility to compensate the slight deviances from a prefect surface.
Screenshot shows the vertical column using an oval gib to lock and locate the column(Lathe bed and headstock block not shown)
Alan

« Last Edit: March 18, 2021, 08:07:25 AM by jackary »

Offline vtsteam

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Re: Stepperhead 2
« Reply #13 on: March 18, 2021, 11:18:14 AM »
Thanks Alan for the explanation of how the groove might be measured for truth.  :beer:

I also believe that there's a difference between nay-saying and the honest curiosity aroused when something new is presented, and I hope that positive questions presented with respect can even be seen to be of value sometimes. In the former a person wants to challenge or belittle, and in the latter a person just wants to understand. No drawing can explain fully what a person envisions, nor can any inventor fully imagine all possible situations or issues, and questions help fill that gap for both.

I was once called in to a job interview as a technical writer. It turned out at the interview that the job was really for patent writing. Though I needed the job, I declined it as not qualified. I was hired anyway by the CEO as a project engineer, so, apparently, honesty wasn't a detriment to employment. But I did do a fair amount of research into patent writing requirements after, mainly for personal reasons. I was eventually discouraged from patenting as not worth the effort for an individual by Don Lancaster's internet postings on the subject. I now think there are better ways to profit from ideas. I don't know if you've looked at Mr. Lancaster's site already, but I think it's good to get that  perspective on what's involved with not only obtaining one, but also profiting from it, and defending it.

Anyway, off that subject, I'm going to admit I'm still a little confused about the gibs and their groove's precision in relation to the round column. So I hope I'm not becoming too tedious. I think I understand that by canting the gib in its groove, it's a means of getting a good fit tangential to a round column. If tangential play is taken up by canting the gib, does its wear surface become  only the corners of the gib in direct contact with the groove?

I realize the cant angle would be small, if fit was good. But would this nevertheless accelerate wear on the gib, when compared to a conventional flat gib (or in the case of a round column ways, a Urwick flat triangular gib) with full contact area?

Or am I totally missing the mark -- the gib isn't canted to take up play?
I love it when a Plan B comes together!
Steve
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Offline jackary

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Re: Stepperhead 2
« Reply #14 on: March 18, 2021, 02:05:48 PM »
Hi vtsteam
This was my explanation and there is no play when the column is locked.

The vertical column grooves would form a full circle when aligned but are purposely mis-aligned to form an offset aperture by the oversize first gib. A secondary gib is added below the first upper gib which can be rotated to urge the offset grooves into alignment, therefore locking the column in its slideway. The gib can have a simple oval profile or be more profiled to match the groove surfaces giving closely matching contact surfaces.

Alan

Offline WeldingRod

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Re: Stepperhead 2
« Reply #15 on: March 18, 2021, 04:48:22 PM »
Yes, the patent process is slow!  My first one took many years.  I had one that got approved without any comments from the examiner; super weird!  We immediately asked ourselves "what did we leave out???"

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Offline vtsteam

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Re: Stepperhead 2
« Reply #16 on: March 18, 2021, 07:57:26 PM »
Still not getting it jackary despite the repetition, but that's okay, no point in your spending more time on it with me.   :wack:  :beer:
I love it when a Plan B comes together!
Steve
www.sredmond.com

Offline BillTodd

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Re: Stepperhead 2
« Reply #17 on: March 19, 2021, 05:33:15 AM »
I'm sure Jackery has something more specific in mind but this is how I'd see it working:

(animated gif - which now doesn't seem to  work on the forum ?)

https://drive.google.com/file/d/17ZOUXsNlswVgdbonc7T0tM3DIl8yyG7q/view?usp=sharing
Bill

Offline jackary

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Re: Stepperhead 2
« Reply #18 on: March 19, 2021, 06:42:32 AM »
Well done Bill thats close enough.
Alan