Unimat SL renovation – any tips?

[rjenkinsgbParticipant @rjenkinsgb]

Hi all,

I recently acquired a rather crusty Unimat SL, which looks a bit non standard but has quite a few interesting parts with it:

There was also a rusty three jaw chuck, a couple of head feed pinions/levers(?) and another three tooolholders for the quick change toolpost.

I’ve fully stripped it down and I’m part way through checking and cleaning up the various parts.

The extra spindle mounted over it turns out to be a duplicate headstock in pretty good condition (other than surface rust)!

So far I have the bed cleaned up – that’s all good, even the paint near perfect under the dirt – and the two nasty looking support bars for the second spindle are now rust-free.

The headstock bearings were gritty and rough so replacements are on order for those.

The three jaw chuck freed up enough to dismantle after alternating between DIY rust remover and oil soaks & that now works very nicely, though could do with a cosmetic skim to remove slight pitting, once the whole thing is re-assembled.

Questions:

The leadscrew handwheels are plastic – are there any nice metal ones available?

The cross slide (X axis screw is a bit sloppy in the slide thread. Any fix other than replace the slide?

Any, has anyone any tips or suggestions for improvements or mods while I’m rebuilding it, as I’ve never had any involvement with these before. (I work with industrial machine tools, but not anything like this before).

Thanks,

Robert.

 

[HollowpointParticipant @hollowpoint]

Congrats on the new purchase. They are simple lathes and are easy to work on so I don’t expect you will have much trouble. But I do have one tip for you.

When you change the headstock bearings, be extra sure to note the arrangement of the bearings and washers. The SL uses cupped spring washers and these absolutely must be fitted the correct way around!

In answer to your other question, yes, metal handwheels are available, (from an earlier model) they come up for sale on eBay from time to time.

 

[SillyOldDufferModerator @sillyoldduffer]

Tips, well don’t start with a full-strip down!  Although machine tools aren’t rocket science, they have gotcha potential.   Things like parts damaged on disassembly because it’s not realised they’re held together by two grub-screws, one locking the other, which is hidden underneath.  Doesn’t come apart, so assume it’s stiff, and hit with a big hammer…

Many ways of innocently messing up reassembly, such as gibs upside down, shims missing, belts incorrectly tensioned, motor misaligned, gears in wrong order/incorrectly spaced etc.  Maybe not realising headstock alignment was done in the factory with a big accurate jig, not by eye on a bench.  All stuff experienced chaps cope with, but a beginner rushing in can cause grief.

Also difficult for the forum to tell the difference between problems due to a faulty lathe, misassembly weirdness and learner driver problems.   Better I suggest to run the lathe “as-is” for a while to get a feel for it, and nothing reveals problems like cutting metal.   Then, tackle the problems.

I’m sure in Robert’s case, having viewed his website, that I’m teaching granny to suck eggs, but I think a Unimat SL is complicated enough to justify taking notes and photos during disassembly.   Robert’s existing skills might well make that unnecessary, but…

Read what the excellent lathes.co.uk has to say.

After the lathe is in good working order, there’s a lot to learn.  Turning is a skill:  materials, feed-rate, rpm, choosing and setting the cutter, work-holding and much else.  In my opinion best to start with simple jobs, of which making metal handles for the lathe is one.  It will teach: identifying and sourcing suitable metal (possibly free-cutting Aluminium), that retail metal is horribly expensive, and that the lathe cuts best when operated ‘just so’, a balance found by applying theory to get into the right ball-park, and then adjusting for results.    For example, rule of thumb, RPM for mild-steel is diameter of job in millimetres divided by 10000.     From that it’s possible to extrapolate RPM for different metals and to compensate for HSS vs Carbide (carbide works best at higher speeds and cut rates; reduce RPM for cast-iron, increase for Aluminium etc.)

Although a Unimat SL can cut steel, try to stay with EN1A rather than structural, tool, or stainless steels.   Aluminium and Brass are well inside it’s comfort zone.  Avoid scrap at first unless you know what it is.  Many alloys don’t machine well.

Final advice from me: there are two main beginner mistakes!   One is hammering machines due to excessive expectations, exceeding the capacity of the motor, bearings and drive train and losing precision due to twisting the tool-post and the bed.  Don’t be an impatient gorilla!  The other is “pussy-footing”, that is persistently cutting too gently.  That quickly blunts and overheats the cutter, spoiling the finish, and making it difficult to cut to depth accurately.   The beginner has to find his machine’s sweet-spot by using it.

Dave

 

[BazyleParticipant @bazyle]

In the ’80s there was a series of articles on using and upgrading this little lathe if you can find the issues.

If the cross slide screw  goes into the casting which is worn you can take up the backlash fairly easily. Either find a tap for the thread, or melt plastic around the thread (research ‘Evan nut’) to make a short length of threaded brass, aluminium  or plastic nut, but in a bit of plate bigger than a normal nut. This is NOT to replace the existing thread. Cut it down to about 2 threads and thread it onto the screw on the operators side. Now if you tighten it up it will act as a locknut and lock the screw. Obviously you don’t want it locked, so back off by just enough so it has taken up the backlash. Fix it with a screw in this position – that is why I said make it out of a larger plate.

[Michael GilliganParticipant @michaelgilligan61133]

Grab this pdf

https://www.emco.or.at/index.php/download/emco-bedienungs-und-serviceanleitungen/drehmaschinen/48-emco-unimat-sl-english/file

MichaelG.

[Clock polisherParticipant @clockpolisher]

Good afternoon Robert,

One thing to bear in mind is that the original motor only has an 8 minute duty cycle and gets very hot.

It’s also quite noisy for it’s size.

I fitted a 550w dc servo motor from a sewing machine to mine.

David

 

[duncan webster 1Participant @duncanwebster1]

I know SOD makes no claims to being a mathematician, but his rule of thumb for RPM is odd even by his standards. Take a 12mm diameter bar. He would have the RPM at 12/10000 which is very slow indeed. Try it the other way up, 10000/12 which is ~800, and is about right if using HSS.

[Hollowpoint]

On Hollowpoint Said:

When you change the headstock bearings, be extra sure to note the arrangement of the bearings and washers. The SL uses cupped spring washers and these absolutely must be fitted the correct way around!

In answer to your other question, yes, metal handwheels are available, (from an earlier model) they come up for sale on eBay from time to time.

 

Thanks for that!

I have ordered a new pair of belleville washers along with the bearings, but not removed the outer races from the spindle body yet; it appear the washers are behind those, though I’m not sure if that is the correct location?

I have found the manual for the machine though & will check the correct assembly order when I get to the point of rebuilding the spindle.

 

[SillyOldDuffer]

On SillyOldDuffer Said:

After the lathe is in good working order, there’s a lot to learn.  Turning is a skill:  materials, feed-rate, rpm, choosing and setting the cutter, work-holding and much else.  In my opinion best to start with simple jobs, of which making metal handles for the lathe is one.  It will teach: identifying and sourcing suitable metal (possibly free-cutting Aluminium), that retail metal is horribly expensive, and that the lathe cuts best when operated ‘just so’, a balance found by applying theory to get into the right ball-park, and then adjusting for results.    For example, rule of thumb, RPM for mild-steel is diameter of job in millimetres divided by 10000.     From that it’s possible to extrapolate RPM for different metals and to compensate for HSS vs Carbide (carbide works best at higher speeds and cut rates; reduce RPM for cast-iron, increase for Aluminium etc.)

 

Although a Unimat SL can cut steel, try to stay with EN1A rather than structural, tool, or stainless steels.   Aluminium and Brass are well inside it’s comfort zone.  Avoid scrap at first unless you know what it is.  Many alloys don’t machine well.

Final advice from me: there are two main beginner mistakes!   One is hammering machines due to excessive expectations, exceeding the capacity of the motor, bearings and drive train and losing precision due to twisting the tool-post and the bed.  Don’t be an impatient gorilla!  The other is “pussy-footing”, that is persistently cutting too gently.  That quickly blunts and overheats the cutter, spoiling the finish, and making it difficult to cut to depth accurately.   The beginner has to find his machine’s sweet-spot by using it.

Dave

All points noted, thanks, though I shortened the quite for space saving.

This thing has no gibs, and a rotatable headstock! I have obtained the correct alignment jig pin to set it in line with the tailstock.

The cutting speed & feed info is definitely helpful; it’s several decades since I used a lathe (school engineering department) so definitely out of practice. I’ve got plenty of brass rod & a couple of bits of mild steel to get the hang of it again.

 

[Clock polisher]

On Clock polisher Said:

Good afternoon Robert,

One thing to bear in mind is that the original motor only has an 8 minute duty cycle and gets very hot.

It’s also quite noisy for it’s size.

I fitted a 550w dc servo motor from a sewing machine to mine.

David

Thanks, that is something I was not aware of! I will look at alternate motors.

 

@MichaelG – Thanks, I got a copy of that before going ahead with the purchase! I don’t like things that you cannot get proper service info for.

@Duncanwebster1 – Thanks, noted.

[Grindstone CowboyParticipant @grindstonecowboy]

You may find some of the videos by a chap called “Adventures with a very small lathe” on YouTube useful. I don’t agree with his approach to everything, but overall quite good. He has done some on a Unimat SL e.g. this one.

Rob

Links to https://www.youtube.com/watch?v=tqRUEY4UNgw

[Grindstone Cowboy]

On Grindstone Cowboy Said:

You may find some of the videos by a chap called “Adventures with a very small lathe” on YouTube useful. I don’t agree with his approach to everything, but overall quite good. He has done some on a Unimat SL e.g. this one.

Rob

Links to https://www.youtube.com/watch?v=tqRUEY4UNgw

Excellent, thanks!

[duncan webster 1]

On duncan webster 1 Said:

I know SOD makes no claims to being a mathematician, but his rule of thumb for RPM is odd even by his standards. …

Whoops!  Not odd by my standards, I often get things upside down.   And leave steps out.

Forgetfulness gets me too.  Somewhere I have a printed table of common metal with multipliers based on 10000/diameter, showing RPM adjustments for carbide as well.   The laminated workshop copy isn’t in it’s proper place and I can’t find the digital version either.   Now I can’t share some simple advice without doing a long search.   Aargh!

Thanks for pointing the blunder out.

Dave

 

 

[SillyOldDufferModerator @sillyoldduffer]

I’ve been wondering about Robert’s machine.  Whilst a production Unimat SL is already versatile, this one’s been customised, for example by bolting the gantry in a fixed position rather than moving the headstock, plus a control box providing belt drive to the lead-screw for powered traverse:

My guess is some sort of small-scale production work.   The build quality looks middling but well thought-out.  Could be a competent  amateur upgrade or a jobbing engineer paid to meet a commercial requirement by modifying a small lathe without wasting time on spit and polish.    The control box looks rough but is properly sealed and labelled.    Evidence against production is it still has the original easily overheated motor, which isn’t designed for continuous work.    Maybe instrument making or tweaking O-gauge model railway parts, perhaps for sale.   Shame the history is lost, someone in the past was up to something a bit different, maybe!

The changes don’t detract from the original lathe – powered traverse is good to have.

Dave

 

[EmgeeParticipant @emgee]

The traversing control looks very much the same as I fitted to an SL many years ago, the engraved panel was done on my TH engraver.

When I sold the SL there was no adjustable traverse stop bar fitted neither were there risers fitted to the head and tailstock.

Presently there is no intermediate drive pulley arrangement fitted and the motor drive pulley is fitted in reverse to allow correct speed changing of the spindle.

Emgee

[Michael GilliganParticipant @michaelgilligan61133]

That socking-great-big tool-post would seem to support Dave’s hypothesis.

MichaelG.

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