MARS Atlas Lathe restoration

[onthebeachalone]

I have just taken on a project of restoring, reburbishing or at least getting in working order, an old Mars 'Atlas' metalwork lathe. I'll try to post information and pictures as the project progresses.

Mars details here (http://www.lathes.co.uk/mars/).

Interesting because these were manufactured in Brisbane in the early 1900s. The Atlas is quite a large, commercial model. It looks like the one to the right in the picture of the Mars stand at an Australian machine-tool exhibition during the 1950s at the bottom of the above link.

The first problem is that someone has stripped the teeth on the low-ratio back-gearing lay-shaft gears, presumably by engaging the gear and failing to disengage the direct drive. So my first task is to find someone who can fix that.

[pipeclay]

If you cant find someone in Brisbane to do it for you I may be able.
I would need to have some dimensions of the gears in the headstock that are not damaged ,unless you allready know the DP and PA of the gears.

[onthebeachalone]

Thanks for that. :)

I do have a local gear cutting outfit looking at it. The challenge is that the layshaft is cast in one piece with a large gear (OK) on one end and a small one (with about half it's teeth missing) on the other end. We are still considering whether to machine a complete new layshaft out of a solid block, or machine the damaged gear back below its root diameter, shrink a sleeve over it and cut new teeth in that. The other damaged gear is the large one that drives the chuck and engages with the small gear on the layshaft (when back gearing is engaged). It also has a few teeth missing as a result of the same incident. We will probably have to get a complete new one machined because one face has a substantial rebate and would not provide sufficient backing for a shrunk-on sleeve. Anyway we'll keep poking at it. I am checking out the other various gearboxes and gear trains so we understand the full magnitude of the task.

[pipeclay]

The easist way is to turn the damaged gears off and shrink a piece of cast on recut the teeth,the sleeve should also be pinned just to be sure it dosent move.

With the larger bull gear I normally shrink a steel ring on ,pin it and then recut the teeth.

You dont really require a great deal of material on the bull gear when shrinking the ring on,but it is better if you can have at least 3mm below the bottom of the tooth.

Would probably expect that the PA is 14 1/2 degrees.

Depending on the size of the gears just as a rough guide to repair both gears is around $140.

[markpest]

Can only echo Pipeclay's response.

I have a Mars Great Scot, and went through the same process albeit a while ago. Great to see (yet) another Mars being restored. (I recently came acrosss an invoice for grinding the bedways for $310 in 1979.) Other Forum discussions at http://www.woodworkforums.com/f65/adjusting-replacing-babbit-bearings-mars-great-scot-lathe-brisbane-134688/ (http://www.woodworkforums.com/f65/adjusting-replacing-babbit-bearings-mars-great-scot-lathe-brisbane-134688/) Seems many of these lathes were used in armament production and were marketed as a precision lathe in their time. ie adverts in SMH (1941) http://trove.nla.gov.au/ndp/del/article/17764634?searchTerm=Great Scot lathe&searchLimits= (http://trove.nla.gov.au/ndp/del/article/17764634?searchTerm=Great%20Scot%20lathe&searchLimits=)

Mark

[matthew_g]

I used to have one of those, Probably the same as yours, Mine was ex Australian Defence Force.
Matt

[onthebeachalone]

Thanks. Sounds interesting. I'll put some photos together and post them.

[onthebeachalone]

I used to have one of those, Probably the same as yours, Mine was ex Australian Defence Force.
Matt That's exactly the same. Thanks for posting the picture.

[onthebeachalone]

Would probably expect that the PA is 14 1/2 degrees.Would you mind expanding on what PA means? I'm a bit of a novice at this. :roll:

[.RC.]

PA= pressure angle

[onthebeachalone]

PA= pressure angleThanks for that. Looks like I'm going to learn a lot about gears through this project.

[Bryan]

Gear geometry can get complicated. Diametric pitch and pressure angle are the two main things you need to google/wiki.

[onthebeachalone]

I've added a few pictures a friend took to show the scope of the problem.

[pipeclay]

Looking at the Bull Gear picture it appears that there should be enough meat to remove the existing gear teeth and replace with a new ring.

A lot of the damage to the Back Shaft and Bull Gear on these lathes is caused by the removal process of Chucks etc from the Lathe spindle.

In most but not all cases users will engage Back Gear so as to LOCK the spindle to make it easier to remove chucks etc,at times these may be very hard to remove and sometimes a lot of load is put on these gears,causing them to shear teeth off.

Not saying it dosent occur,I dont believe it is generally caused by someone trying to engage the gears whilst the spindle is turning.

[onthebeachalone]

A lot of the damage to the Back Shaft and Bull Gear on these lathes is caused by the removal process of Chucks etc from the Lathe spindle.

In most but not all cases users will engage Back Gear so as to LOCK the spindle to make it easier to remove chucks etc,at times these may be very hard to remove and sometimes a lot of load is put on these gears,causing them to shear teeth off. Which leads me to wonder if there is a better way of locking the spindle to remove the chuck. I'd hate to get the gears fixed only to have someone strip them again. :doh:

[Bryan]

Which leads me to wonder if there is a better way of locking the spindle to remove the chuck. I'd hate to get the gears fixed only to have someone strip them again. :doh:

Better to rotate the spindle backwards, by hand, with a block of wood on the ways, under a chuck jaw. There's a thread about it here: http://www.woodworkforums.com/f65/having-trouble-unscrewing-chuck-lathe-135107/.

[onthebeachalone]

Better to rotate the spindle backwards, by hand, with a block of wood on the ways, under a chuck jaw. Excellent. Thanks for the suggestion.

[onthebeachalone]

Another half-day working on the MARS lathe today. There's a 3-step pulley as well as a 2-speed gearbox on the overhead shaft arrangement, so there's plenty of speed options. I noticed that there was a lot of play between the input and output shafts of the gearbox so thought I had better check it out to check that all the gear teeth are OK. They're fine, and the oil looked OK but there a bit of sludge in the bottom with very fine metal powder. It just looks like the results of normal wear over many years but I decided I should clean the whole thing out as part of the project.

It was a bit of a struggle removing the input shaft due to burrs caused by the grub screw fixing the 3-step pulley. Fortunately we have a hydraulic press so not an insurmountable problem.

It is now completely dismantled. All looks in good nick inside. The only issues arising were that the 3-step pulley had one grub-screw missing and the other one was loose. The grub screw fixing the clutch fork in the gear change spindle was loose. Not major problems as everything is keyed and I can ensure they are tight when reassembling.

I took a few pix of progress.

[onthebeachalone]

Most of today's efforts were cleaning the gearbox inside and out and re-assembling. It was previously used in an old flour mill so most of the dirt on the outside ins 'flour and oil paste', almost like pant, and no amount of cleaning solvent will move it.

The old oil gasket was looking pretty scrappy so I made a new one before re-assembling.

Putting it all together again was really nice. There seems to be very little wear and everything clicks into place perfectly. :2tsup:

Back next week to fit the gearbox back onto the lathe.

[onthebeachalone]

The last two Tuesdays I have been concentrating on dismantling the headstock spindle and cleaning all the parts. With a lot of care most of it came apart pretty easily until I got to the bull gear with the broken teeth. It is keyed to the spindle and positioned against a shoulder on the short (LH) end, so there's a long piece of shaft along which it must be extracted... and it won't budge. We put it in to 20 tonne press and took it up to 2 tonnes. Stuck solid. We were reluctant to apply too much more pressure for fear of damaging either the gear or the spindle. If left it soaking on the parts washer until next week.
I did some measuring to determine the available metal on the damaged bull gear. The overall height from the rebate to the top of the teeth is 11.5mm. The rebate to the root of the teeth is 5mm, so there is only 6.5mm of 'meat' under the teeth. Need to consider whether, for the sake of three missing teeth it might be better to build up replacement teeth rather than strip off all the good teeth and shrink on the ring for re-cutting. The fourth picture shows roughly how they should mesh.
Next I started on the feed screw drive train which also has a gear with a couple of broken teeth.
The final picture is of the lathe overall in its current state.

[franco]

Your first photo in post #13 shows a repaired tooth two teeth to the left of the missing one. This is a very common and acceptable repair for an occasional missing tooth in a back gear bull wheel where only one tooth is missing. Probably would not be a good idea to do two or more successive missing teeth this way though. It is done by tapping the wheel, screwing in two small studs and filing them to the shape of the missing tooth.

Why not do the other missing teeth this way and avoid having to disturb and possibly further damage the bull wheel? A Google search for repairs to back gear teeth will turn up several examples of this technique, and some other alternative successful repair methods for dealing with single tooth replacements which don't involve removing the bull wheel from the spindle.

Some time ago I assembled descriptions of half a dozen different gear tooth repair methods from various internet forums - if you would like a copy PM me with your e-mail address.

Frank.

[onthebeachalone]

Your first photo in post #13 shows a repaired tooth two teeth to the left of the missing one. Thanks for pointing that out. I hadn't spotted that it was a repair. I just assumed the tooth was only partly broken. I'll have a better look at it next Tuesday.

[onthebeachalone]

More progress today.
First priority was to take some careful measurements to start discussions on the best way to fix the back gearing layshaft.

I've drawn these up in Turbo-CAD for clarity. I haven't done gear contours in Turbo-CAD before and, sure enough, when I come to do it I need to know:
Number of teeth (easy)
Diametral Pitch
Pressure Angle.

Obviously I have counted the number of teeth and have measured the root circle diameter and the addendum circle diameter. I'm wondering how to work out the Diametral Pitch and Pressure Angle, other than by trial and error until I get a fair match.

Any suggestions appreciated.

[franco]

Diametral Pitch = (N+2) / OD where N is the number of teeth on the gear and OD is the outside diameter of the gear.

Gear formulae: http://www.engineersedge.com/gear_formula.htm

The gears on a lathe that age will almost certainly be 14 1/2 degrees pressure angle. If you have a look at Post #14 in this thread:

First Time Gear & Keyslot Cutting - The Home Shop Machinist & Machinist's Workshop Magazine's BBS (http://bbs.homeshopmachinist.net/showthread.php?t=50009)

There is a diagram showing the tooth shapes for various pressure angles on a 40 tooth 20DP gear which gives an idea of how the tooth shape should look. It is probably worth reading the whole thread for the general gear information in it.

Frank.

[onthebeachalone]

Thanks Franco,

I proceeded with the trial and error approach and got something that looks OK (below).

Now I understand the maths better and have got my head around how Turbo-CAD does gears, I'll have another go with the correct calculations.

Cheers,

[onthebeachalone]

If you ever wondered how to fix a gear with broken teeth, just ask pipeclay. He did a beautiful piece of work on our broken back-gearing lay-shaft.

Before and after pictures below.

Thanks for your help, mate. :2tsup: Just like a bought one!

Back on the job tomorrow starting to repair the odd missing teeth on a few other gears.

[SC_RUFCTR]

Great thread. I hope to do nothing but stuff like this when I'm retired. (maybe just a little travel as well)

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That's an impressive lathe!


I used to have one of those, Probably the same as yours, Mine was ex Australian Defence Force.
Matt

[morrisman]

nice repair job ..... 10 out of 10 MIKE

[RayG]

Hi pipeclay, nice repair, very neat and tidy. any details on the process?

Regards
Ray

[pipeclay]

Damaged area is machined down enough to accomadate a new piece of cast.
A suitable piece of cast is faced and bored to suit,and then shrunk onto the existing shaft.
This is then finish machined to size and the gear teeth cut (at this stage you hope that your mandrel set up dosent move ) unfortunately mine did, so that piece was machined off and another piece fitted and the mandrel set up alltered.
After cutting the teeth the new gear was drilled and selock pins used as a secondary retainer.

[Auskart]

Very nice work.

[onthebeachalone]

That's an impressive lathe!...and right next to it is an even bigger, older one. It's too big to be of any practical use in our workshop and it ain't going anywhere because it was placed on the slab before the shed was built around it. The bed is 3.5 metres long and the chuck is 450mm diameter (with plenty of room for a bigger one).

Goodness knows where it came from or who made it. No branding that I can see. When I've finished getting the MARS in working condition I might give the old one a coat of paint to make it look like it works.

[onthebeachalone]

No photos, but a major project over recent weeks has been to fully dismantle the gearbox on the front of the carriage, clean out all the swarf, refurbish various spring-loaded detent balls and replace some more missing gear teeth Now fully reassembled and everything turning smoothly.

Today's project was to remove the thread cutting gearbox and clean that out. It proved to be impossible to access two of the mounting bolts without raising the lathe bed. Fortunately we have an engine hoist that can handle the weight but took the precaution of removing the motor first to help keep it reasonably balanced.

Underneath the bed was a 60 year accumulation of swarf so now is an opportunity to clean all that out. Inside the gearbox was also full of swarf but fortunately all the gear teeth are in good nick so it's just a matter of giving it a good clean and again refurbishing various spring-loaded detent balls.

Shouldn't be too long now before we can start reassembling the beast,

[markpest]

Well done - it's amazing what you can find when you do an archeological 'dig' under the bedways. Looking forward to next installments - and of course the pics when you have a moment. Mark :2tsup:

[onthebeachalone]

Well, my MARS lathe restoration project has progressed to the point where it is operational and being used for some 'real' work (as distinct from producing some replacement parts for itself). All the broken gear teeth have been replaced by screw studs filed to a fair profile which seem to mesh OK without any 'clunks'. :roll:

I think I have discovered the cause of at least some of the 'mashed' gears I have had to fix. It appears that someone must have used the automatic feed and failed to notice that there was some obstruction to the carriage movement, perhaps some material left lying on the bed. Once the carriage ground to a stop against the obstruction, several feed gears lost some teeth.

That's all fixed now but on testing after reassembly I found that there is also damage to some teeth on the feed rack on the front of the bed, no doubt just at the point where the obstruction occurred.

The damage is not all the obvious visually, especially since I tried to re-profile the teeth slightly (with a file):no:. Now there is only a slight bump noticeable when using the hand-feed or auto feed to move the carriage. However, it is a serious problem when screw cutting as the carriage is then driven by the half-nuts clamping on the feed-screw. This means that the pressure is on the reverse side of the rack and pinion teeth and they jam quite severely.

I would appreciate any advice on how to fix these teeth. It's a bit of a pain because the rack is screwed and pinned and I will need to take the carriage off again in order to pull the rack of the pins.:mad3:

I have tried to highlight the damaged teeth in the attached picture.

[onthebeachalone]

When I've finished getting the MARS in working condition I might give the old one a coat of paint to make it look like it works. The decision has been made to dispose of this very old, heavy duty lathe if anyone is interested. More pictures here (https://picasaweb.google.com/108825063001911260279/OldLathe?authuser=0&authkey=Gv1sRgCNnzmsae97a44gE&feat=directlink). Not the MARS one, the even older, bigger, one here (http://www.woodworkforums.com/f65/mars-atlas-lathe-restoration-141925/#post1414757).

[pipeclay]

If the rack is the same as the involute gear dp that I cut there maybe enough room to get in there with a small die grinder and dress the side of the rack.

If its to hard to get clear access you will have to remove the rack (probably easier in the long run).
Do the teeth just need cleaning/dressing.

If you have access to a shaper you maybe able to clean the teeth up with a tool ground to suit,dont think it would need to be perfect.

If no shaper you could use a pedistal or radial drill if you have one of suitable size,just gind a suitable tool up place in the chuck,spindle in low gear or locked if possable and just raise and lower the quill,the hardest part will be working out your work holding,not hard really just need to put some thought into,( a parallel clamp and shims to adjust depth of cut,the pressure of the cutting tool will hold it from moving).

[onthebeachalone]

Thanks Pipeclay. As far as I can see the teeth are somewhat deformed (as in bent rather than broken). I think they would need some building up before they cold be re-shaped. It is surprising how severe the jamming is (and only in one direction) considering the apparently small amount of deformation. There are two very definite points on the rack where the it occurs.

Meantime the lathe works fine so long as we don't try to do any thread cutting.

I'll probably have to remove the rack sometime and clean it up so I an see more clearly what the exact problem is.

Thanks for your help with the back gearing by the way. It all meshes beautifully.

[Bryan]

As a work-around could you wind a string around the carriage wheel shaft with a weight on the end, to keep the teeth loaded the right way? Just so you could screw cut if needed.

[Ueee]

Hi,
I'm a bit surprised by the damage you have on the rack. I have the same lathe only later, from the 50's, and i have crashed her a few times:C but every time the flat belt drive has slipped before any damage has been done. Having said that i have not crashed her with the back gear in and the extra torque may do damage before the belt slips. I plan to make a new rack and pinion for mine anyway as the feed is a bit course, something like 37mm (i use metric as all the dials/screws on mine are metric, but every other part on the machine is imperial) per turn, and it lacks feel. I was planing to cut a new rack on the shaper.
One of the annoying things i have fixed is the gear and shaft that drives the cross feed. It is helical as it is driven by a worm, but it was free to float back and forth in the apron. This meant every turn or change of direction with the handwheel the gear would clunk against the apron. I just made a few bronze "shims" (about 1/4" in all) to hold it in place.