Slideway problems

[JimM]

Hi all

Now I'm finally starting to use my miling machine (after 18 months of ownership !) I'm finding the shortcomings of inexperienced buyers purchasing second hand machinery. The machine is an Elliott Omnimill and my biggest problem is that the Y axis appears to have a fair bit of wear. No matter what I do I can't seem to adjust the tapered gib to give me more than 3 inches of free movement - if the gib is set whilst the table is forward it locks up when you wind it back towards the column and if adjusted whilst the column is back then the table is very loose when brought forwards. I've currently got it set at the mid point but still only really get half of the travel I should.

Any suggestions of anything I can do to improve matters - I suppose the best solution would be to get the slideways re-ground but I suspect this would be very costly and a real pain as I would presumably need to get the saddle & table off ? Does anyone know of a hobby friendly company that may be able to do this on site ?

Alternatively is there any way to use shims to remove the worst of the problem. My thinking was that the shim would need to be in the middle of the slideway but would it go behind the gib or need to be attached to the fixed surface somehow. Also can't work out how I would I measure how much of a shim I need

Or is there something I'm missing and there's possibly something else other than wear that’s causing my issues.

Cheers

Jim

 

[Blogwitch]

Jim,

It sounds as if your tapered gib is 'floating', that is it is not locked up at both ends if it is a double screw system, or if a single screw system where the adjusting screw fits into a slot milled in the gib, the cause is usually the slot has enlarged lengthways, and is allowing the gib to slide backwards and forwards as you move the table, so locking the table up tight in one direction, and going slack in the other. The cure for that is usually dress the gib slot to nice and square, and make a new screw with a tightish fitting head in the slot.

Tapered gibs can be a little finicky to set up initially, but once you have them in the correct position, I find they can't be beaten.

Don't forget, always plenty of lube in there. Metal to metal contact can cause all sorts of nasty problems.

Bogs

 

[JimM]

Hi Bogs

Thanks for the reply.

Before you read the next bit can I just ask that don't take it the wrong way, I really appreciate your input and having nothing but respect for you but I just couldn't phrase what I wanted to ask without it sounding like I was questioning your advice

The gib on mine does have a slot but it also has a screw at the end which butts up against the gib to lock it into place. I've double checked and both screws were already as tight as I could get them presumably removing the possibility of a floating gib. Also even if it was floating would it not be the case that it would lock up when the table was moved away from the column and become looser as moved towards it? Lastly with a floating gib would I be able to get 3" of movement, why wouldn't it lock up quicker than that? Again no criticism of our suggestion is intended I'm just trying to understand how the machine works.

On that subject can you clear up one point for me on how they fit fit together. I'm assuming the faces of the fixed slideway are (or should be !) parallel and that the sadlde has a taper on the gib side slideway ? When the gib is inserted the tapers face each other so that the other side of the gib is then parallel to the knee as in the attached pic.

One final point to mention is that the gib does look a bit battered, I suspect it may have been dropped at one time in it's life as there is a chipped area along the bottom edge although from what I can see this edge doesn't actually touch anything so I don't think it's affecting it - or would you think otherwise ?

Cheers

Jim

 

[Blogwitch]

Jim,

Don't worry about yourself querying what I am saying, I am not there to actually see and feel your problem, so I can only go by my experience with such things. That is one of the major problems when working thru a forum, everyone will all have their own theories and experiences, and because we can't all be there with you physically, poking the problem with a stick, you just have to take what suggestions are thrown your way, and hopefully, one of them will cure your problem.

What I told you in my last post are exactly how I cured the problems I had.

It was about two years ago, just before I got rid of it, that I had exactly the same problem as you are having (except mine was happening in the opposite direction), and it was on my old mill/drill, on the Y axis. Mine didn't have the back screw, only the slot and screw, and by doing what I said, making a wider headed screw to fit in the gib slot, cured the problem completely.
With my new lathe, after a few weeks use, the cross slide started to do the same thing, but the reverse of your direction. The far end gib screw had come loose, and a few minutes later, after getting them both adjusted correctly, things have been fine ever since.

So as you can see, that is why I suggested the two methods. Unfortunately I didn't pick up on the direction movement of your problem, none of us are perfect.

BTW, before going any further, have you made sure the table locking screws are well out of it before adjusting up the gibs?


Now back to your problem.

I can't remember how the tapers worked on mine, because the table had been taken apart at least 18 years before, when I stripped it down for servicing after purchasing it second hand. But I would agree with your sketch as to how it worked.

Now because you have checked the operation of the adjustment, and all seems to be as it should, but the problem is still there, suggests that the problem is being caused by something else, maybe just a chunk of swarf stuck in the wrong position, and maybe embedded in one of the internal faces.

You are lucky that the problem is in your Y axis, in that it is usually the easier of the two dovetails to get into, and to solve your problem, maybe the easiest way would be to screw the whole table off in the Y axis and flip it over, so you can get to see what is happening. Again without actually being there, to see how it all comes apart, it is difficult to say how easy it will be to come off.

Getting someone in to put things right just might cost more than what the mill is worth. So it is always best to see if you can fix it yourself. If you have someone who is spanner wise to help, if you are not already, then it really is a fairly simple and logical job to get the machine down to basics.

By going by general rules of mill builds, you will have a bearing block just behind the Y axis winding handle, with a couple of screws holding it to the top dovetail.

Once those screws are removed, when the handwheel is turned, the leadscrew should screw out, leaving the table in position. Then by removing the gib strip, the whole table should be able to be maneuvered until it lifts off and is able to be turned over for a quickie peek at the workings (get a friend to assist). Sometimes there is something on the far end of the leadscrew to stop it being wound thru the leadscrew nut. In that case. remove the nut, splitpin, bolt or whatever to allow the leadscrew to be taken out. It maybe sounds a monstrous exercise to a newbie, but it is really an easy, but bulky, job to do.

Once the table is off and upside down, everything will be laid bare for you to measure up and inspect for you to solve the problem of the sticking gib. You will also be able to easily measure up the main casting dovetail to make sure that is parallel. If it is as should be, then you can concentrate on looking for the problem on the top half of the dovetail, and again, with the gib in it's correct position, it is an easy job to check that the two running surfaces of the dovetail are parallel. If not, then it would most probably be a slight machining job on the gib strip to get everything running smoothly.

If you do decide to take the table off, and you need a bit of advice about how and where to measure up, just ask.

Bogs

 

[New_Guy]

just a thought but most of the work is done in the center of the mill so why not crank the tale right to the end to use the least worn part of the table

sorry if this was all ready mentioned i didnt read all this thread

 

[joeby]

Jim,
It seemed rather odd that the problem you are having is (as I understand) over the travel length of the Y axis. Usually, the most-worn area on a milling machine is near the center of the travel, causing the table to be loose there and tight at either end.

After doing some looking, it appears that your mill is like this one:
http://www.lathes.co.uk/elliottmillers/page2.html

This type of Y axis with the screw off center of the ways will cause the slide to twist as it moves. The left side of the slide (on the pictured mill) will try to move first, with the right side lagging behind.

The gib could be worn into a "rocker" shape causing some of your trouble or, at the very least, making an adjustment almost impossible.

The drawing you made is what I would expect the ways to look like, and you can see that the gib is easily pulled out after removing the adjusting screw from the "big" end. I would start there and check the gib to see how flat the working surfaces are.

Another point to remember is that the gib needs to be adjusted while in full contact with the way. If you were to adjust it with the gib overhanging the front of the way, you could easily get it overly tight.

Kevin

 

[kf2qd]

Anather possibility is that the ways are worn a bit, front to back. Are these dove-tail or square ways? a couple pieces of round stock and a set of large calipers (I am assuming you don't have any huge mics, a large dial or digital caliper would do) and measure at several points along the the slide to see if there is any taper.you then might have to figure out which end is worn and then work out the other end with file and stone. (probably not the best sounding suggestion, but it would be the start of restoring the machine, and a lot less money involved than replacing it...) It would also be a good place to learn some rebuilding/restoring/maintenance skills that may well come in handy later on another machine. Just measure and check everything before you rmove any metal.

Anybody on the forum with experience live close?

 

[JimM]

Hi guys

Firstly thanks for all the advice and input

I think removing the table is going to be the best option, it doesn’t look too bad a job I was just being lazy and hoping that I could get round that. The wife and little’un are away for Easter so that may be a good time for me to tackle it, I’ll be able to spend the time I need on it without interruption.

However in the meantime I think I will give some attention to the gib itself. If I lay the gib on the table of the milling machine (the closest thing I have to a flat surface) I can see light between the two so it does look like that it’s not completely flat. Only looks to be a couple of thou but presumably the gib is a precision item so should be spot on ? Can I lap this flat using a piece of glass and wet & dry, what grit papers should I start and finish with and should both side of the gib be done or just the ‘sliding’ side. I’ve got some brass shim stock so if need be I can make up any lost material if it ends up too thin.

Cheers

Jim

 

[Blogwitch]

Jim,

Before doing anything to do with metal removing from the gib, I would suggest you get the table off first.

You might find you need a couple of thou to play with when you check them out together, and if you have already removed it, problems might arise.

If it is curved as in bent, rather than being curved as in worn (measuring along it with a mic should soon show it up, if the measurements are the same along the length, it is bent), and that is a totally different matter, and that can usually be straightened with three small bars and a vice, plus VERY gentle pressure. That should be done before mating the two together.

Bogs

 

[JimM]

Hi Bogs

Please correct me if I'm wrong but I don't think I'll be able to 'measure' for bentness/wear as the taper of the gib will give different readings along it's length anyway.

Cheers

Jim

 

[Blogwitch]

Sorry Jim, misunderstood yet again.

I have never seen a gib bent along the tapered edge, only along the thickness edge.

In that case, ignore what I said about straightening.

But I would still leave everything alone until you get the two edges fitted together, so that you can definitely see where the fault is, then see what action is required to correct it.

If the main casting is perfectly OK, then a little bit of right angle maths and you could soon make another gib strip to put everything back to spot on, if you had a mill to do it with.

Bogs

 

[JimM]

Cheers Bogs, sure it's more down to my explanations than your misunderstanding.

Just for 100% clarification I've attached my C-O-C pic of the gib, the dotted lines show where I can see light between the table and gib (obviosuly can't see both sides at once!)

However before going any further I'll follow your advice and get the table stripped down, will post back here when I get that far !

Cheers

Jim

View attachment gib.pdf

 

[Blogwitch]

No problems Jim.

I would think that the nibbled bit you showed on the end wouldn't even come into play.

Also, don't worry about making new or remachining your gib strip. I have done a lot of all sorts of types in my time, and although they look dificult to make or machine, they really are very easy to do if done logically and with a little bit of common sense. But as I said, you won't have a machine to do it on, so that has to come into your figurings as to how you will achieve it.

Also there have been a fair amount of changes most probably since your machine was built, and a change of material might be on the cards to obtain a longer lasting and smoother operating gib. There are now a lot of modern day plastics that would be cheaper to use, and well able to stand up to the stresses required.

Bogs

 

[SAM in LA]

My circa 1994 lathe has straight gibs with a set screws on each end and a large screw with a handle in the middle. What made a huge difference in my case was simply sanding the gib so that it was nice and flat and smooth. I used various grades of wet/dry paper on top of a mirror tile so I had a nice flat surface. I also cleaned and lubricated the mating surface on the lathe bed. Just another option.

SAM

 

[d.bick]

Jim
Try a 1/2" lenght of shim of a few tho thick between the gibb and the saddle at the adjusting end this may reduce the slack in the slides if it works you will know what sort of gibb you need to machine and will have the mill to do it on.
Dave Bick

 

[JimM]

Hi all

Now that the wife and daughter are away I've had a chance to look at this again. I've taken the table off, surprisingly easy job ! and had a good poke around. There wasn't any obvious signs of anything stuck in there so I've measured across the saddle dovetail and it does look like there is some wear there.

As you can hopefully see on the attached image it goes from 5.954" at the back to 5.944" at the front. I've also attached a diagram of how I measured the width but I've only been able to measure the gib side of the saddle as I haven't got a bar the right size to use to measure the other side.

Any suggestions on the best way to help minimise the problem. I have some brass shim stock of various sizes but not sure if I could use this as presumably the shims would need to be between the gib and saddle and would therefore be liable to move as the table was slid back and forth.

Thanks

Jim

View attachment Measure.pdf

 

[Mo deller]

Hello Jim, just after having seen this post I saw an ad for Elliot omnimill spares on this site and thought you may be interested.
http://www.homeworkshop.org.uk/

Peter.

 

[don-tucker]

only one answer to this one,and thats remachining,sorry
Don

 

[Davo J]

Hi Jim,
I wouldn't go off the edge of the dovetail it will give you a false reading. You could use the shank of a good drill bit, something around 1/2inch would do. You need to measure with a precision round on each side to give a true reading.
Dave