Unimat 3 carriage feed screw – material used.

[Julius Henry MarxParticipant @juliushenrymarx92355]

Hello:

Posted by Kiwi Bloke on 28/06/2023 12:22:43:

May have misunderstood, but the 'proper' thrust bearing should be on the left side …

Indeed, I misunderstood / misread by me.  8^°

The OEM arrangement for that function (thrust bearing) uses part of the surface of the leadscrew end against the left side of the steel bushing: (sorry for the untidy sketch)

ie: steel against steel.

… may be other possibilities for getting some new bits that can be modified …

Indeed … Food for thought.

I will have to change the design for the part to be screwed on to the right end of the new leadscrew I ordered and also new bushing. I have a whole 60 days to think about it.

Posted by JasonB on 28/06/2023 13:13:59:

… the thrust is coming from the other direction so you really want the cutting forces to push against the thrust bearing so it needs to be on the left of the bearing.

Right, now I get it.

Otherwise all it is doing is giving a bit of preload.

Yes, that and a smooth turning surface for the handwheel to land on.

Thank you both for your input, much appreciated.

Best,

JHM

Edited By Julius Henry Marx on 28/06/2023 19:09:40

[JasonBModerator @jasonb]

Also consider that if you take the bearing out to 6mm you will have even less surface where the side of the bearing and step on the 8mm screw run together so less area to take load = more likely to wear

[Julius Henry MarxParticipant @juliushenrymarx92355]

Hello:

Posted by JasonB on 28/06/2023 19:30:42:

… if you take the bearing out to 6mm you will have even less surface …

Quite so, even less. Making a bad design worse.

Which is why I will have to think about a different, probably more complex design for the feedscrew / new bushing arrangement.

Thank you for your input.

Best,

JHM

[Kiwi BlokeParticipant @kiwibloke62605]

I think there's a risk of over-thinking this, and inventing new ways to polish a t*rd. Given the limitations of the rest of the machine, I'd suggest that the addition of a thrust washer either side of the bush is probably enough. Incidentally, I'd think the bush is cast iron or bronze (can't remember), not steel.

However, if you want to go all fancy, ball thrust bearings are available in 5mm ID, 11mm OD, 4 or 4.5mm axial thickness. IIRC, the bush is 12mm OD, so the bearing assembly can still be loaded into the machine from the right side. You'd need to shorten the leadscrew thread, and extend the end of the leadscrew, but you're committed to most of that already. You's also need a simple shield around each thrust bearing. I'd guess this would be the trickiest bit, but a stepped-bore tubular shield could be pressed or Loctited onto the non-moving part of each thrust washer.

Oh, forgot, Oriental bits ordered. No doubt the same approach would be possible…

[Dave SParticipant @daves59043]

On my Unimat the simple addition of some molyslip grease to the end of the leadscrew once in a while, combined with careful adjustment of the hand wheel/acorn locknut gives totally acceptable results. The forces on the leadscrew are not large, and a roller thrust bearing is overkill.
That the LH end (headstock end) is “floating” makes square root of a gnats fart difference, all the thrust and guiding accuracy is between the bed end (tailstock end) and the saddle nut.
Over constraining the leadscrew by adding tight fitting bearing blocks to both ends is imo a bad engineering decision.

[Graham MeekParticipant @grahammeek88282]

Hi Jason,

A good move with the counterbore.

Regards

Gray,

The standard design has lasted 40+ years without modification. It is clear there are some issues with "backlash" and normal wear. Inserting a thrust race at this point is an overkill given the cutting forces involved. Two 11 mm O/D 5mm I/D Ball races in a new Bearing Housing would be more than enough to cope with the forces involved. Provided they were not over tightened in the quest for zero back-lash.

There is a down side to such modifications. The leadscrew or feedscrew experiences a certain amount of drag from the original set up. Remove that drag and the feedscrew or leadscrew could move during the cutting operation due to vibrations.

Another thing to watch out for when purchasing non-original parts are the "Limits and Fits" in operation in the country of origin. The "New" replacement leadscrew could well be smaller than the original Emco one. It could also be larger which may mean it will not screw into the existing hole and there-in is another problem.

The M8 x 1 LH taps used by Emco might well be H6 tolerance, the far eastern manufacturer might use a H7 tap. In both cases the feedscrew would be rolled to match the tapped hole to maintain the correct "Fit". Or visa versa.

Regards

Gray,

[Julius Henry MarxParticipant @juliushenrymarx92355]

Hello:

Posted by Kiwi Bloke on 29/06/2023 04:20:40:

… risk of over-thinking this …

Yes, I agree. It is very easy to fall into that hole.

… suggest that the addition of a thrust washer either side … | … bush is cast iron or bronze …

Does not seem to be bronze so it could well be cast iron. Thanks for that bit.

… if you want to go all fancy, ball thrust bearings …

Not really, just want it to work as well as possible. The thrust washers will probably do well enough.

Thank you very much for your input.

Best,

JHM

[Julius Henry MarxParticipant @juliushenrymarx92355]

Hello:

Posted by Dave S on 29/06/2023 07:30:37:

… addition of some molyslip grease to the end of the leadscrew … | … careful adjustment of the hand wheel/acorn locknut …

Yes, I also use grease but the careful adjustment of the hand wheel/acorn locknut was not possible till I made the modification to the handwheel. For the time being it works smoothly, much better that before.

… forces on the leadscrew are not large, and a roller thrust bearing is overkill.

Could be. I have come to think that overkill is usually (not always) highly dependent on the end result.

eg: while drawing up the Unimat 3, someone at Emco thought that manufacturing the carriage in the same material as the bed was overkill, that an adjustable tailstock was overkill and that having a replaceable leadscrew nut made from a suitable material was also overkill.

And here we are. 

Over constraining the leadscrew by adding tight fitting bearing blocks …

I agree. I make sure there is no tightness and that the feedscrew turns freely.

Thank you for your input.

Best,

JHM

Edited By Julius Henry Marx on 29/06/2023 21:09:35

[Dave SParticipant @daves59043]

The guys at Emco were concerned with engineering solutions.

Elegance in engineering is mostly the art of compromise.
Would a cast iron saddle on a lathe of that size work?

Certainly, my watchmakers lathes and Super Adept both have cast iron parts there.
Would it work better than one made from mazak?
Probably not, and certainly not if you also factor the cost in.

The Unimat is a nice little lathe, but it’s also a cheap little lathe. Cost is a major factor in making something sufficiently not shit which is also useful/ will make a profit.
If cost is no concern then different compromises apply.

Im (possibly unfortunately) of the general opinion that working well enough beats perfect every time.

The leadscrew bearings I wasn’t especially concerned with rotation constraints but rather length ones.

I’d need to check, but I’m pretty sure the leadscrew on my CVA (a not insignificantly engineered Toolroom lathe) is only axially constrained on one end. I don’t think that was a cost decision given the machines end use…

[Julius Henry MarxParticipant @juliushenrymarx92355]

Hello:

Posted by Graham Meek on 29/06/2023 11:34:54:

… has lasted 40+ years without modification.

I beg to differ. If what I have read on the web is correct, my Unimat 3 was manufactured in 07/1980, 43 years ago this month. Apparently it was discontinued in 1990, which (if accurate) would make it 10+ years without modification, at least from Emco.

From what I have seen in exploded parts diagrammes, Sieg made quite a few modifications to what they manufactured based on the original Emco design, never seen one save in photos so I cannot speak of quality.

That said, I have seen a great many U3 modifications published/shown on the web and I am sure there are many more that have not been published.

I believe that (one of) the most interesting ones is Maurice Rhode's, followed by your take on the feedscrew nut and tailstock modifications.

… 11 mm O/D 5mm I/D Ball races … | … would be more than enough … | … Provided they were not over tightened in the quest for zero back-lash.

Both Kiwi Bloke and you agree that it would be the best solution, so that what I will attempt to do.

… a down side to such modifications.

Yes, I expect there is, as always.

Remove that drag and the feedscrew or leadscrew could move …

Thnaks, I'll have to keep an eye on that then.

… purchasing non-original parts … | … leadscrew could well be smaller than the original …

Yes, it could well happen. But I don't think there's a way to get a brand new OEM part these days and for the US$36 this Sieg part cost me, I thought it was worth seeing what I could get from this manufacturer.

Better that than risking my pension money on a perfect state, very little use, no returns accepted etc. sample from the usual suspects on flea bay.

And then, there's also the present state of the thread on the leadscrew post to take into account.

… taps used by Emco might well be H6 tolerance, the far eastern manufacturer might use a H7 tap.

I had some idea but only when I purchased my U3 did I realise just how exponentially expensive precision can be. Having experienced the results of U3 Emco manufacturing of the U3, I can only say that I have serious doubts with respect to what tolerances Emco may have used viv-a-vis the ones used by Sieg in their C0 version of the U3.

Thank you very much for your input.

Best,

JHM

[JasonBModerator @jasonb]

10years without Emco altering the design shows they got it about right first time and another 30 years for the likes of me, graham and others to not see a need to alter either.

Not sure the modifications of the C0 are an improvement over the U3, the leadscrew does not even run in a bearing on the C0, just straight in the block!

The Emcos (I have a U3 and used to own an Ecomat8.6) are better built that the Sieg etc machines. If the U3 were available today it would probably cost 3 times what a C0 costs.

I also doubt that the "Sieg" part you are buying is actually sourced from the Sieg factory more likely an aftermarket part that will hopefully fit C0 lathes

 

Edited By JasonB on 30/06/2023 07:45:23

[Graham MeekParticipant @grahammeek88282]

I had one of the first U3's in 1976. As far as I can remember the U3 continued in production until the introduction of the U4 1997?? which marked the 50th anniversary of the Emco-Unimat. This was just before the Millenium edition, I also have a U4 leaflet with Pro Machine Tools email address on so that has got to be quite recent, 2002??.

Original U3 parts can still be had at Holz & Hobby, Austria. (As posted previously). This includes a complete carriage assembly.

The bearing you are saying is steel should be a Sintered bearing, which may appear to look like steel but it is definitely not. I cleaned up the face of the one in my U3 during restoration. I took off barely 0.1 mm and the material came off exactly the same as machining Sintered Bronze or an Oilite bearing. Perhaps some previous owner thought his modification of a steel bush was better? Sadly we will never know.

As a time served Toolmaker some of the YouTube offerings fill me with horror from an engineering viewpoint. Just because something is on there does not mean it is good. Making the modification is up to the individual. If that person is unsure then it pays to come to a Forum like this where countless years of knowledge, and learning by making similar mistakes can be given on the subject. It is after all free advice, but like all advice it can be ignored.

Lastly for quite a number of years during my 45 year career I earned my living using Emco machines. Not once did those machines let me down. Nor did I have a single job returned as being incorrect. The customers by the way ranged from Aerospace, Motorsport, Optical through to Surgical aids. That does not include the countless Myford Super 7 Handwheel dials I supplied to Neil Hemingway. The users of these may well be reading this.

Emco did after all give us the first mass produced Bench top CNC and PC machines, they were, as always ahead of the game.

Regards

Gray,

 

 

Edited By Graham Meek on 30/06/2023 11:45:10

[Julius Henry MarxParticipant @juliushenrymarx92355]

Hello:

Posted by Dave S on 29/06/2023 21:37:34:

… Emco were concerned with engineering solutions.

I am quite sure of that, as sure as that at one point the accountants were given a say in the matter. Probably marking the moment when elegance in enginering morphed into compromise.

Would a cast iron saddle on a lathe of that size work?

In my limited design experience (architect) with various materials, my opinion is that it definitely would.

… my watchmakers lathes and Super Adept both have cast iron parts there.

I seriously doubt that they would have used Mazak.

… better than one made from mazak?
… not if you also factor the cost in.

One thing I have learnt is that reducing costs while at the same time compromising basics is not a good choice.

… Unimat is a nice little lathe, but it’s also a cheap little lathe.

In have an undated *.pdf file containing part of a larger catalogue from a company called Blue Ridge Machinery and Tools, in the US offering a basic Unimat 3 (U3, driving plate, lathe dog, 2x dead centers, tool holder, service tools and instructions) for US$345.00. Adding steady rest/3-jaw chuck/six tooks and live center made it a US$499.00 deal and a further addition of vertical head/milling table/drill chuck and a set of drilling tools made it a US$725.00 deal.

Just to get an idea, in April 1980, you could get a hot dog+small Coke in downtown Manhattan for US$1.00 and these days just the hot dog goes for no less that US$5.00 and a small coke ~US$3.00.

… of the general opinion that working well enough beats perfect every time.

As I see it, the problem is that well enough and perfect are highly subjective concepts. In my field of works it always makes for a permanent discussion topic with clients and developers.

Thank you very much for your input.

Best,

JHM

[Julius Henry MarxParticipant @juliushenrymarx92355]

Hello:

Posted by JasonB on 30/06/2023 07:05:46:

Not sure the modifications of the C0 are an improvement over the U3 …

No idea. Like I have previously mentioned, never seen one, only looked at the diagrams and mentioned that they were a few modifications.

… doubt that the "Sieg" part you are buying is actually sourced from the Sieg factory …

I really cannot say. The store deos sell Sieg lathes/mills and most every part for what they sell. I will have to wait till it arrives and compare it to the OEM one.

Thank you very much for your input.

Best,

JHM

[Julius Henry MarxParticipant @juliushenrymarx92355]

Hello:

Posted by Graham Meek on 30/06/2023 11:43:32:

… one of the first U3's in 1976. | … U3 continued in production until the introduction of the U4 1997 …

I'm sure you know more about the timeline than I, so I stand corrected. Thanks for clearing it up for me.

Original U3 parts can still be had …

Yes, I have seen their web page. I was not able to get a reply from them when I emailed asking about a feedscrew nut for the U3's saddle, so I made one from SAE68 bronze.

The bearing you are saying is steel should be a Sintered bearing …

I'll check on that when I take it apart again.

Not once did those machines let me down. Nor did I have a single job returned …

All that does is speak (very) highly of your knowledge and expertise as a tool maker, knowledge and expertise which allowed you to use a U3 for your professional work in spite of its shortcomings.

It also speaks of your degree of professionalism as a contractor. ie: you did not supply a good enough part, you supplied what for you was a perfect part. One with your name and reputation behind it.

That said, I think that wanting to know about the material used by Emco to manufacture the U3's carriage leadscrew may be slowly but steadily moving into what could possibly constitute contentious territory.

My opinions on the U3 are from a newly arrived retired professional (from another field of work) with no prior knowledge of what it was about. I only speak (with or without reason) of what I discovered after purchasing it.

So I will pause this thread now and come back (or start another) once I receive the new leadscrew and draw up/turn a new right hand bushing that I can test and report on.

In the meanwhile, I still have other U3 things to work out and will continue to seek advice here at ME.

Once again, thank you (all) very much for your input.

Best,

JHM

[Graham MeekParticipant @grahammeek88282]

Contacting Holz & Hobby to ask about the materials used is never going to get a response. They are just a spares outlet for Emco machines.

If you need detailed information then you need to contact the Emco Technical Dept. However given the age of the machine the drawings for this I know are in storage and cannot be accessed by the Technical dept. I have tried recently.

The material will probably have a Werkstoff number with no direct comparison to UK specs and possibly SAE.

This material would need to have good cold working attributes as well as have a certain degree of work hardening. This last quality is one of the reasons to go down the Thread Rolling route as the thread form will be stronger and harder than the parent metal. It is however not the only reason to Thread Roll. This is another cost consideration which is settled at the design stage, by the Designer, not the Accountant.

Designers are constantly searching for the most economic methods of manufacture. Making things of Cast Iron is all well and good but this has its drawbacks when the section of the material gets as thin as the Carriage on the Unimat 3. Using Cast Iron here would probably mean using the Shell Casting Technique to get consistent results, an expense in itself. Sand casting would probably need more material and require machined datums later to hold the part, another additional cost factor. Both methods would also require a Heat Treatment process to remove any hard spots due to one part cooling quicker than another. This is an additional cost and we have yet to start machining. Contraction of Cast Iron is greater than that of Zamak, (to give it its proper name), thus the part would need to be cast larger than required. The weight of the Cast Iron is another factor which needs to be taken into account by the Designer, when it comes to dispatching 1000's of the finished item all around the world. Those extra Schillings for carriage would need to be taken into consideration when the initial cost of the machine was settled. Which is usually before pencil is put to paper.

I dread to think of the cost of machining this part from solid Cast Iron and any designer worth his salt would not consider this on a mass produced part. The Unimat 3 predecessor the SL sold over 300,000 units and we are not taking into account the copies made around the world.

A comparison of Zamak against Cast Iron shows very little difference in the mechanical properties. It has slightly better damping qualities which is good for such a small machine. I would also suspect the tensile properties would be greater.

As regards the short comings of this machine I don't see any. The only limiting factor I see with this machine is my imaginative use of the machine.

Just to correct one point. I have only recently returned to my Unimat 3 following the donation of a much modified/abused and worn out donor machine. Thus I did not use it to earn my income.

The Compact 5 I have, has been with me a number of years and complimented my Emco Maximat Super 11, Emco F3 and Emco FB2. These last 3 machines are all with new owners.

Emco were not the only machine tool manufacturer to use Zamak, not wanting to agitate the owners of these machines I will not mention these manufacturers.

I trust you will take this resume of Engineering Design in the spirit of learning something new about how Designers reach the end product.

Regards

Gray,

 

 

 

 

Edited By Graham Meek on 01/07/2023 11:54:25

[Julius Henry MarxParticipant @juliushenrymarx92355]

Hello:

Posted by Graham Meek on 01/07/2023 11:52:18:

As regards the short comings of this machine I don't see any.

Given your knowledge and experience in these matters, I cannot but accept your point of view as the most valid one.

… will take this resume of Engineering Design in the spirit of learning something new …

Of course, there is no other way. 8^)

Thank you very much for taking the time to write it up, much appreciated.

Best,

JHM

Edited By Julius Henry Marx on 01/07/2023 13:47:28

[Kiwi BlokeParticipant @kiwibloke62605]

General point, emphasising what the wise Graham Meek wrote, a few posts back.

Feedscrew bearings, ideally, need to have zero axial float, should rotate smoothly, with no torque variation around the circle, and they must not bind (stick-slip phenomenon). It's all very well trying to get a low-friction bearing, but definite drag is needed, to keep the screw from rotating, as a result of vibration, and not helped by unbalanced 'balanced' handwheels. This 'unwinding' is a particular problem with coarse-pitch, small diameter screws (eg Myford cross-slide), because of the unfavourable helix angle. But it can also afflict screws with less steep helix angles, and provoked Graham M to make a lock for his Maximat's cross slide screw. It can therefore be useful to have a bearing arrangement that can be pinched up or pre-loaded to provide (consistent) drag. Apparently simple things can get complicated, when there are conflicting requirements…

[Graham MeekParticipant @grahammeek88282]

Hi Kiwi Bloke,

Some very valid points as regards stick slip and free rotation. It is a misconception that zero backlash is the best. If there is no play then there is no room for the lubrication film and this leads to accelerated wear. This wear then leads to backlash and the cycle continues. Whereas a regularly lubricated bearing will last for years without any adjustment.

On the Emco FB2 the instructions for setting the feedscrew backlash at the factory. This was set at 0.05 to 0.1 mm.

Regards

Gray,

Just a little point in passing as regards the cross-slide feedscrew nut on the U3. Backlash can be greatly reduced in this nut simply by using the taper of a screw driver blade to rotate the nut slightly before locking it up with the countersunk screw. I have found the blade is best inserted on the tailstock side of the cross-slide. With the adjustment being carried out on the least used portion of the thread.

Although the backlash has been reduced, because the nut has been rotated slightly there is always a reservoir of oil on the side of the nut not in full contact with the thread. Simple but effective.

Regards

Gray,

[Kiwi BlokeParticipant @kiwibloke62605]

Posted by Graham Meek on 02/07/2023 12:43:00:

…

On the Emco FB2 the instructions for setting the feedscrew backlash at the factory. This was set at 0.05 to 0.1 mm.

…

Please excuse this swerve off the original topic…

Graham, a space for lubricant in a plain thrust bearing makes sense, even if it results in axial float, However, with rolling element bearings, this float can be eliminated with impunity. I'm surprised by Emco's instruction, given that the FB-2's screws are supported by a pair of deep-groove ball bearings. Perhaps the instruction was to prevent gorillas applying too much pre-load to bearings with limited thrust capabilities. Any ideas?

[Kiwi BlokeParticipant @kiwibloke62605]

Oh Bother! I'd just shut down the computer, when I realised I'd misunderstood Graham Meek's post. My misunderstanding is frequent – according to my dear wife… Anyway, it's the morning here, and I haven't had coffee yet, so you can't expect much sense yet.

Graham's reference to Emco's backlash adjustment presumably includes backlash in the nut, which must, of course be lubricated reliably, requiring space for the lubricant. In my earlier post, I was confining comments about axial float to the leadscrew support bearings only. Here, it seems reasonable to aim for zero end-float – easily achievable with rolling element bearings, but not simple with plain bearings.

Apologies for the confusion.

[Graham MeekParticipant @grahammeek88282]

Hi Kiwi Bloke,

You have redeemed yourself, the misunderstanding was not helped by me not being more specific and mentioning the feedscrew nuts in my comment.

The comment about gorillas over-tightening the bearing end-float is another good point. I have replaced more of these bearings for friends who have purchased secondhand machines than any other bearing on the FB2. Once set at the factory these will need very little attention. It could be many years before these ever need adjustment and this will depend on the amount of use the machines get per day.

Regards

Gray

 

Edited By Graham Meek on 03/07/2023 10:37:03

[Graham MeekParticipant @grahammeek88282]

One Tip I forgot to add with regards to the U3 Cross-slide feedscrew. I have modified the slotted M4 countersunk screw. Using a Ball Nosed slot drill as close to my grease gun nozzle as I could find. A depression is made in the head of the countersunk screw to just below the depth of the screwdriver slot. A small hole about 1 to 1.2 mm is then drilled through the length of the screw.

Grease can now be applied to the feedscrew in the centre of the feedscrew nut. The action of which forces any debris from the nut as the new charge of grease is applied.

I have not found this weakens the screw in the course of usage.

Regards

Gray,

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