Unimat 3 saddle gibs

Hello:

I am having quite a few issues in my Unimat 3 and one of the causes is lack of rigidity in the saddle.

While I may be expecting too much from the U3, I have read more than one post stating that replacing the glass filles plastic saddle gibs in the Unimat 3 for hard brass made a world of difference.

I would happily choose SAE6X brass but locally I can only get that in round stock which is out of the question as it would mean an absurd waste of time, effort and money.

The counter guy at my local non-ferrous metals purveyor I has suggested that, given the size and small/limited forces at play where the new gibs would go ie: under the U3's carriage, that I make the strips from 7075-T6 aluminum which has has in 4.0mm thick stock.

Not only that, he is also willing to cut and sell me the ridiculous amount I'll need, something essential for me.

Seeing that the original gibs are made (?) from 43 year old glass filled plastic, I think this is what is commonly called a 'no-brainer' but I would much appreciate an opinion on those in the forum who know about this.

Thanks in advance.

Best,

JHM

Edited By Julius Henry Marx on 09/06/2023 21:06:03

I can imagine no convincing argument against it … so I commend the idea.

MichaelG.

Im with Michael but what's SAE6X brass?

Hello:

Thanks so much for the prompt reply.

Me neither, but what do I know? 8^°

Good ...

For the time being, the ayes have it.

Another issue is just how much adjustment ie: how tight these Unimat 3 jibs have to be.

This is not a real lathe where the carrier/saddle stays in place more or less on it's own weight.

With the U3's saddle weighing relatively nothing, it seems to me that the ways (specifically the front/piramidal one) do not do much to to keep it in place, depending quite a bit on how tight the gibs are and their own geometry when in place.

eg: the distance of the gibs to the inside edge of the ways

Meaning that they have a say (so to speak) in how well the U3's Z axis maintains its perpendicularity to the X axis.

Make sense?

Thanks in advance.

Best,

JHM

Hello:

Thanks for pitching in, that's two ayes then. As an interested party, I cannot vote.

Sorry, I meant SAE6X bronze ie: any of the SAE bronzes I have read about. ie: SAE68, SAE64, etc. 

Best,

JHM

Edited By Julius Henry Marx on 09/06/2023 23:04:08

The gibs need to keep the play at a minimum. If there is on even wear along the bed, these elastic gibs will partially compensate for that. When using brass or aluminum gibs, the carriage will get stuck.

I would first try to set the play at a minium and check the result.

I have made brass gibs for my mini lathe. Any type brass will do.
If I have to do it again, I will try POM gibs because they don't wear down the bed. This allows me to set the play to zero and probably the carriage will be hard to move at some points. But that is only for a short time until the POM gibs are wear down a bit.

Is the bed cast iron like most other lathes? If so, mild steel will work well for gib strips. It is what most other lathes use. Steel against cast iron is a good bearing combination.

I would use brass, I don't know how to explain, but aluminium can be a bit "gummy" when used in such a way. The surface of the metal being so soft that it can sort of smush and foul up. Probably depends on grade.

They aren't complex parts so why not make and try both? Or if you are feeling a bit more experimental you could try an idea I had a while ago of using ball bearings. The idea being you could then tighten the "gibs" almost as much as you want without causing too much friction.

.

… 7075-T6 aluminum which has has in 4.0mm thick stock.

MichaelG.

.

https://www.smithmetal.com/pdf/aluminium/7xxx/7075.pdf

https://en.wikipedia.org/wiki/7075_aluminium_alloy

Edited By Michael Gilligan on 10/06/2023 09:23:30

+1 with hollowpoint, any sort of Brass would be preferable to Aluminininium. Even the original GFN wasn't a really good choice but cost/value comes into the equation and despite the EMCO name, it's not a heavy duty turning machine, the later versions of the original, built to a price.

Regards Ian.

I would not consider aluminium as a good choice against cast iron, steel or brass/bronze.Noel.

I am not familiar with that lathe but from what I can tell from your pics, those are lift plates, not gib strips. Mild steel is what most lathes use there. The gaps you  have circled mean nothing. The inverted V of the "prismatic" bed is what provides the alignment, not the lift plates. Lift plates are just there to hold the carriage down on the bed without tipping if the cutting tool is stuck out in front of the carriage etc.

If for some reason you particularly want brass, you can get brass in many sizes of plate and flat bar from model engineer suppliers and online. As you have found, bronze is hard to find in plate or flat bar, as it is more common in round bar, used for making bushes etc. So try searching for brass rather than bronze.

But mild steel will make a stronger, less flexible part and will bear against a cast iron bed just fine. That is why most lathe manufactuers use it.

Edited By Hopper on 10/06/2023 10:03:11

That would be my concern, and it's why Aluminium isn't used as a bearing metal.

Bearing metals are generally used in pairs, one a bit harder than the other, but both slippery. Cast-iron and mild-steel, Cast-iron and Brass, Steel and Brass, Steel and Bronze etc.

Not used in plain bearings as far as I know : Lead, Copper, Tin, Stainless Steel, Aluminium.

That the Unimat uses Fibre-glass gibs is a new one on me! I don't know why they would do that. Is it something clever like PTFE rather than ordinary fibre-glass?

My guess is Aluminium gibs will tend to scrape and stick rather than slide and they'll suffer a high wear rate. Made worse because exposed Aluminium is attacked by air. Normally the reaction quickly forms an impermeable Oxide layer that stops air getting at the raw meta and all is well. But I think the oxide layer will be scraped off whenever an Aluminium gib moves, allowing air to eat freshly exposed metal, yum yum. Aluminium Oxide is also an abrasive, - corundum, not ideal in a slide.

Little to be lost by trying Aluminium, though I'd use Brass, which is almost certainly suitable. Bronze is over the top for this, hard to work, and expensive.

Where are you Julius? In the UK it's unusual for a walk-in metal dealer to sell small quantities of metal other than from an off-cut box, and not always then. They're set up to deal with big trade orders, not bits and bobs, and aren't particularly helpful to folk doing their best to not spend money! Model shops are better for small quantities and big DIY stores often carry a range of metals, including brass rod and strip, for decorative purposes. Pricey by weight, but they sell small quantities. Otherwise, the internet is your friend, provided of course, that the delivery system works, and you don't get whacked with customs duty and tax! (My friend in rural Thailand reckoned half his post disappeared.)

Dave

Aluminium is too soft. It will get bit bits of hard swarf embedded in it and act like an abrasive hone rubbing up and down your lathe bed. Brass could do that to a lesser extent too, being somewhat softer than steel. I'd guess that is why most lathe manufacturers use steel for lift plates such as this.

I have a U3, I think they are nylon, they are a bit stiffer than I would expect from bog standard nylon so perhaps some kind of fibre reinforced nylon? I've seen the same stuff used in RC cars and gears.

I replaced mine with brass rectangular bar of unknown alloy.
whilst 7075 is one of the harder alloys I would use mild steel or cast iron in preference.
sort of Brass > Iron based metal > aluminium based metal.

Whilst your there also do the cross slide gib.

Not sure where in the world you are, but DIY sheds (B&Q etc) often have eye wateringly expensive small bar stock.

You could probably hack a suitable piece of iron type metal from a small car brake disk

Dave

My Unimat 3 restoration, (see my album), uses the same Gib strips that were originally fitted, but just turned over. I personally would not use Aluminium for this application. Brass would be my only substitute.

Rubbing the existing Glass filled Gibs on some Wet or Dry will also restore the surface.

For what it is worth, the Compact 5 uses exactly the same set-up as the Bedway profile is the same on both machines.

Regards

Gray,

Edited By Graham Meek on 10/06/2023 11:07:35

I'm with Graham on this one, you can turn the plates around 180 degrees to a new non worked face, then when it needs tightening again turn it over and before you sell it turn it around again, the only worn part is around 3mm wide at the edge. As said the same material was used on all Emco 5 manual and cnc lathes, link to video showing the easy method of access to the Z plates on a cnc 5.

**LINK**

emgee

Hello:

First, a big thank you to all who pitched in.

@Huub

Yes, I have thought about POM/Delrin/Teflon and such but getting small quantities of the stuff is an issue.

I will look into it again.

@Hollowpoint, @Circlip, @noah shelley

I had not thought about the the very strong points against using Al of any sort @SillyOldDuffer makes in his post. As an architect with a long practise behind me I should have thought about all that, particularly the fact that Al2O3 is one of the most popular abrasives used to manufacture sandpaper ...

@Hopper

> ... lift plates, not gib strips.

Thanks for that. I have seen them refered to as gibs most everywhere. I stand corrected.

> Mild steel is what most lathes use ...

> ... gaps you have circled mean nothing. The inverted V of the "prismatic" bed is what provides the alignment ...

I see.

There is an alignment problem in my U3. I have tested it by just puting the saddle on the bed (no lead screw or plates) to try to see exactly what it was about and pressing a bit on top of the saddle reduces it to practically nought but (as you know) the forces at play when turning a part can be quite high. ie: much higher than what I can excert with my hand while holding the carriage in place from above.

After that and reassembly with the plates tightened, things seemed to get better which is why I thought that maybe the edge of the plates needed to be nearer to the bottom of the ways to help with the alignment but I still have to test it while turning a piece.

Q: How can I test this properly? ie: what lack of rigidity is acceptable / what are the limits of the U3 in that respect? Sometimes I think I am pretending too much from what I am starting to think of as an expensive toy.

> ... get brass in many sizes of plate and flat bar ... ... bronze is hard to find in plate or flat ...

Indeed. Not hard, impossible. I have asked: it would have to be cu$tom ca$t and the minimum quantity is 500kg.

> ... mild steel will make a stronger, less flexible part and will bear against a cast iron bed just fine.

I'll also look into that.

@SillyOldDuffer

Like I mention above, you make a straightforward case against aluminium so I have ruled it out. I will look into other metals (brass, steel) and POM, Teflon and such and see what I come up with.

> ... something clever like PTFE rather than ordinary fibre-glass?

Cannot say for sure. I read about the OEM Unimat 3 plates and their being replaced by metal ones on-line, with report of very good results.

> Where are you ...

Most of the time, here: 34.6037° S, 58.3816° W. Shipping from anywhere is expensive and as in most places where import taxes are applied, shipping costs are part of the taxable amount equation.

@Dave S

> ... also do the cross slide gib.

That's the first thing I did after taking it apart and seeing the sorry scrap of metal the previous owner was using.

> ... eye wateringly expensive small bar stock.

Yes, funny money prices. It is rather a relief to see that my everyday experience in sourcing materials to fix my U3's problems is not limited to an owner on this side of the world.

> ... suitable piece of iron type metal from a small car brake disk

A very interesting idea. From a small car may be too thick and need milling to get things to size, but one from a small motorcycle or even a bicycle may have the 4.0mm max I would be able to use.

@Graham Meek

> ... see my album ...

Yes. I have read your interesting post quite a few times.

Your solution to the worn out carriage lead nut is by far the best solution to Emco's lack of sound engineering criteria* I have seen after scouring the web for months on end. It is also a permanent solution as a worn nut can be replaced with a new one in under 5' and may (?) even provide the possibility of using a different type of lead screw without the inherent runout a plain M8x1 thread has.

*Another example being the impossibility of making any sort of adjustment to the tailstock, something I think you have addressed in another post.

But I digress ...

I was under the impression that you had made a new set from brass but maybe it was just the cross slide so I will try to see if I can dress the OEM plates and see what I can get from that.

@Emgee

> ... turn the plates around 180 degrees to a new non worked face

Yes, I'll try that out first. But these OEM lift plates are already > 43 years old, maybe a modern synthetic material (if available) such as brass filled Delrin/Teflon would work better. I really don't want to have to to this more than once.

Right then, I think that settles it: no aluminium or bronze for the reasons given. Reworked OEM lift plates or new ones from metal / special friction free material it is.

Once again, thank you very much to all those who shared their experience/knowledge with me.

Hopefully I will be able to make good use of it. 8^)

Best,

JHM

Edited By Julius Henry Marx on 10/06/2023 14:28:35

Small bicycle brake disks tend to be stainless steel of one sort or another. The central flange of most car disk brakes is quite thin, and probably of sufficient size.

Dave