Unimat 3 saddle gibs

The rear Gib Plate on my Emco Maximat Super 11 was made of the same material. This lathe was 36 years old when I let it go this time last year. In all that time I only ever adjusted that plate once. I know a lot of potential buyers were put off by the use of plastic on this particular lathe, but that machine never once let me down and was still capable of some very fine work when I reluctantly let it go.

There is very little load on these plates, they are there just to keep the play to a minimum and keep the parts together. The geometry of the bedways is such that all cutting forces are taken on the upper surfaces.

If you can vertically lift the carriage assembly away from the bedways then no amount of new Gibs will rectify this. It is time to either rework your existing carriage as I did, or obtain a new or good secondhand unit.

Regards

Gray,

Hello:

I see.

No! - Gods forbid, not that. With the gibs adjusted there is no perceptible vertical movement even if I try to lift the bed by the carriage.

But (I still have to test it again, after adjusting the plates and see what's up) there was some perceptible movement from the perpendicular in the carriage ie: between axes X and Z.

But ....

How can I test this properly?

And in doing so, what lack of rigidity is acceptable or within the limits of the U3 in that respect?

Thank you very much for your input.

Best,

JHM

If you are getting non-vertical perceptible movement of the carriage on an inverted V-way bed, it is most probably down to the fit between the inverted V-way on the bed and the V-groove in the carriage.

First suspect would be small bits of swarf have worked their way in their and are holding the two surfaces apart. Second would be some small burrs on either surface. Third would be wear.

You could check it by taking the carriage off and cleaning things thoroughly. Then apply a very very thin smear of engineer's blue to the bed and then rub the carriage up and down it once or twice and then see from the blue spots on the carriage where it is contacting. IT should be fairly consistent over the full length of the contact area. If not, it will need scraping to match, which is a whole other can o' worms.

Some years ago, I obtained an apparently unworn, probably barely used, U3, in a grubby, but not rusted condition. After a complete strip-down and clean, I tried to turn some approx. 3mm dia. MS stock. It was hopeless! It transpired that the mating surfaces of the underside of the saddle held the 'lift strips' a tiny bit away from their ways on the bed, so the saddle could move vertically. Some careful blueing, and needle-file work on the saddle soon had them snug. Problem solved. Check yours!

Emco may have cut corners occasionally, for the accountants, but I think they usually had a good reason for most design decisions. They were not averse to using MS gib strips, so I'd think that the plastic (glass-filled nylon?) was chosen for an engineering reason, rather than cost. Perhaps because of the difficulty of ensuring adequate lubrication? The material is quite hard and stiff, and is secured close to its working surface, so I suspect that cases where they seem defective is the result of the manufacturing fault I've described, or wear - or even simply being loose.

Don't forget, if it is GFN, the filler is GLASS. Invariably the filler is randomly oriented and glass tends to be harder than adjacent materials so scratching occurs. If not filled, the moulded faces of Nylon would exhibit better wear properties than a 'machined' surface.

Regards Ian.

.

I am always cautious about questioning your assertions, Ian … but I would like to see evidence that “Invariably the filler is randomly oriented”

My own experience is that many such parts are made by an injection process which naturally aligns the glass rovings.

Importantly, though: I have never seen the component in question … and would be very interested to see one sectioned and photographed.

MichaelG.

As you are no doubt aware Michael, in injection moulding, swirl is induced into the plastic so linear orientation cannot be guaranteed. Linear alignment is controlled by either extrusion with long strands or lamination of a woven matt. Problem with GRP mouldings is that if the outer surface is damaged, exposing the strand fibres, they become carriers of water along their surfaces leading to delamination. doesn't apply with GFN as the fibres are so small.

Regards Ian.

Happy to accept that, Ian

… let’s just put it down to a difference in semantics

MichaelG.

The Plastic Gibs are intended to sit slightly lower than the mating face of the bedway. When tightened they are pulled down slightly, while the free end bears against the bedway. Before I machine the U3 carriage to remove wear. I checked the step between and unworn part of the carriage working face and the Gib Mounting Face. This dimension was 0.03-0.05 mm smaller than the thickness of the rear bedway.

When I re-machined the working faces I replicated this dimension. By taking some material off the Gib mounting face. Parting off 12 mm Mild Steel on this lathe is no problem as long as the carriage clamp is on.

Thus the first check would be to measure the gap when the Gibs are tightened in situ on the carriage and the thickness of the rear bedway. If the Gap is larger it will need attention, if it is the same or smaller, then leave well enough alone.

A lot depends on how fine the glass fibres are chopped up. I tend to think of this material in the same way as a hand scraped surface. The high spots left by the scraping process are the the exposed glass fibres. Around these fibres small quantities of oil accumulates just as with the scraping. However given the colour of the material I would not be surprised if it was not already oil-impregnated. Thus it would be to a certain extent self lubricating.

Are you using HSS tools or Carbide inserts?

Regards

Gray,

PS was typing this as Ian's reply came in.

Two very good questions!

My start with a mini-lathe didn't do well until I learned to blame TOM. That is, the need to keep an eye on the three main reasons things go wrong. They are:

• T for tool. Plenty to go wrong on a lathe, especially one with a long history! Worn slides, bearings, screws, half-nut, and chuck. Twisted bed, bent spindles, toothless gears, set belts. Also, many opportunities for maintenance, and getting maintenance wrong - gib adjustment, noting the things go one way round and are often dimpled; blocked up oil-ways (greased when they need oil); swarf jambing the works, and adjustments: bearing preload, gear selector, and even tailstocks can be fiddly to get right. But on the whole, I think tools get more blame than they deserve, because even indifferent lathes can produce good results.
• O is for Operator. The operator causes most of the trouble in my workshop! I'm self-taught, so lots of mistakes, painfully slow progress, and re-inventing the wheel. The list of operator errors is endless; wobbly work-holding, not locking unused axes down, not realising cutters are blunt, choosing the wrong type of cutter, getting RPM, feed-rate and or depth of cut wrong. Cutter not on centre-height, or with excessive overhang. Spinning work hitting something. Not realising work, cutters and the lathe can all bend. Pushing the machine too hard is a common beginner mistake. Hobby lathes, especially small-ones, aren't built for removing metal quickly. In the worst case a heavy handed operator will damage the motor, electronics, and drive-train. And if he gets away with that, the machine wears rapidly, and loses accuracy because it bends due to the cutter being forced into the metal. Pussy-footing is bad too - excessive caution rubs the cutting edge, blunting it quickly. Not obvious that edges last longer taking deepish cuts at a suitable feed rate - it's because optimum cuts tend to preserve the cutting edge by wedging metal off the job just in front of it. The operator has to find the sweet-spot.
• M is for material. Many metals do not machine well. The gremlins infesting my workshop caught me out good and proper by filling my beginner junk-box with unsuitable scrap - all of it. Soft sticky Aluminium that tears. Gritty steel, tough hardened steel, work-hardening stainless, chilled cast-iron, a length of super-grabby bronze, hard brass, seamed pipe with a hard weld running down it. Thing is, quite a lot of manufacturing is done with processes other than machining. Unfortunately there's no guarantee metals selected for stamping, rolling, grinding. extrusion, casting, forging, drop-forging, welding, plating, corrosion resistance or heat-treatment will cut on a lathe. So I recommend beginners start by buying metal known to be machinable.

Worst case is a self-taught beginner starting out with a worn or maladjusted lathe and a box full of unsuitable metal. The combination can cause a lot of problems, such as trying to part-off stainless steel held in a bell-mouthed chuck with a blunt cutter!

So, back to first principles - what exactly are you trying to do Julius? Could be a combination of difficult material and inexperience are asking too much of the lathe. With luck the answer is easier than replacing the gibs.

Dave

Hello:

Yes, I magined so. It is slight but it is there.

I have the feeling that the lead screw backlash does not help.

Everything was throroughly cleaned. As for burrs, I would have to check.

I was planning of doing something like that but have no EB, I will try with a one of those *permanent* solvent based Sharpie markers.

Right. Will do that ASAP.

A really very frightening proposition. Way above my pay grade.

Thank you very much for your input.

Best,

JHM

Hello:

I will have a closer look at those surfaces.

I first lapped the surface of the plates on some worn 800 grade paper but then decided to turn them over. Things improved quite a bit.

As I have mentioned in another post, I am an architect by trade, not an engineer. That said, the only Emco products I know first hand are the U3 and the (M1?) milling head/table, both purchased second hand roughly a year ago.

I am in no position to argue for or against the use of glass filled synthetics for gibs and such. But after taking apart the U3, the M1 milling head and X-T table and seeing how much effort was put into limiting the type and amount of materials used (eg: underside of the carriage (!), lead screw nut post, etc.) I am absolutely convinced that accountants and not engineers were in charge.

I have gone to re-read most if not all the articles/posts I poured over before deciding to purchase the U3 and not one of them mentioned that the lead screw nut was not a replaceable part. It would certainly have been a deal breaker for me.

But things are what they are and that is what I have to work with. With the help I am finding here at ME, I'm certain I'll be able to make the most of it.  8^)

Thank you very much for your input.

Best,

JHM

Edited By Julius Henry Marx on 11/06/2023 14:05:19

I have "scraped" the saddle of both my lathes. For scraping I used a diamond dremel disk (not the dremel) and sanded the high spots on the saddle (not the bed) only the flat side, not the V shaped side!
I measured the tilt on the saddle edges using an indicator and stopped sanding when the indicator did not move when I pressed on the edges of the bed. I used the sharpy method to find the high spots.
After sanding with the Dremel diamond disk, I sanded the sides using a 1000 grid paper.
It is a time consuming but "easy" job and it will improve the rigidity and accuracy of the lathe. It is also the first thing to do before aligning these parts.

I did the same with the head stock and tail stock of both my lathes.

Hello:

I do not use a parting tool as I have not found a suitable one yet. I have seen a couple of interesting designs but have yet to decide on one. For now, I have been able to get fairly proficient at parting via the careful use of a well tesioned hacksaw with a 32 TPI blade. Locking the carriage clamp was something I discovered early on.

Will do.

Lacking any cutting tools and wanting to get started, at first I sent for a few Carbide tools and inserts+holders. I've had mixed results with both, the new 200W DC motor being a huge improvement.

I am now awaiting for delivery of what I have been advised are reasonable quality 6mm HSS pre-formed tools. I expect they will do till I'm able to grind my own.

Thank you very much for your input.

Best,

JHM

Edited By Julius Henry Marx on 11/06/2023 14:24:19

You need non-drying engineers blue, not drying marking blue or layout blue. Stuarts Micrometer Blue is one brand, if it is still available.

But if as you say in another post, you are at the stage where you have not yet learned to sharpen your own HSS tool bits, then your problems with finish are most likely due to operator technique than any problem with lift plates or V ways or other parts of the lathe and you are probably best to leave well alone for now.

Hello:

Yes, can't ask for what is simply not there.

Indeed ... 8^D !!!

So I have come to learn.

Being mechanically oriented and confident in my manual dexterity (if you will) the first order of things for me was to take it all apart and thoroughly clean up everything, piece by piece. As you may imagine, this immediately lead to replacing the headstock bearings, the cross-slide gib, attempting to reduce the axial play in the carrier lead screw and doing something about the hand-wheels, tasks which are for the most part finished.

Indeed, but in the hands of an experienced machinist.

Yes. In another life I worked a few years in IT and PICNIC (problem in chair not computer) was the culprit over 80% of the time.

I can fully relate to that.

Yes, guilty on all counts.

These last ones are the worst ones as the damage they can cause can be important.

Also guilty.

Quite so.

I am slowly but steadily finding my footing. As in most things in life, experience is paramount but something to be acquired as transmisison is always difficult, sometimes impossible. And then, many times, only the hard way.

eg: I can properly identify most unusable stuff such as soft sticky Al, seamed pipe or metals that look / feel as they cannot be used. But I have work-hardened steel. Lack of proper training and dull / inapropiate tools have played an important part.

But I have had good luck with a piece of SAE68 bronze I am using in an attempt to machine a new led screw nut for the cross-slide which has an incredible amount of wear.

Can't help being self-taught, time and patience will fix that but I am slowly making progress fixing a worn lathe with adjustment problems. Eventually, I guess.

See next post ...

Edited By Julius Henry Marx on 11/06/2023 16:09:42

... continuation:

At the moment I am in the process of turning a new lead screw nut for the U3's cross slide from a 25mm piece of 100mm long SAE68 (?) bronze stock. Rather sloppy in its manufacture (uneven surface+a bubble taking up about 7.0mm of the total length) but an unbeatable price.

Adjusting the lift plates has made quite a difference. If I can manage to get this part done and working properly, another problem will have been solved.

Next in line are carrier lead screw wear which I seem to have (partly/temporarily) solved with the contraption below and headstock / tailstock alignment which I think is a can with a great many worms in it.

Undoubtedly so, I'll try my best to deal with it. I have been in worse situations before. 8^)

Thank you very much for taking the time to write up such an interesting and thoughtful post in answer to my questions.

It clearly and very accurately reflects my personal experience with the use of the U3.

In my opinion, it should be a 'sticky' at the very start of the 'Beginner's questions' section of ME and labeled as mandatory reading for any beginner, especially if they are owners of a Unimat 3 or similar.

Best regards,

JHM

Edited By Julius Henry Marx on 11/06/2023 16:28:39

Hello:

I don't think that is available locally.

Is there any other type of ink/marking liquid it can be substituted with?

I'm sure of it and I'll keep it in mind. Won't be mucking around just because.

Thanks for your input.

Best,

JHM

The paint should not dry so quickly. You can use an "art painters oil based paint" that is available in small quantities. Any dark (Blue, Red, BLack) colour will do.

Hello:

Best,

JHM