Unimat milling table - post modification

I had the same problem on my Dore-Westbury milling machine i.e. loss of registration on slackening the collumn clamp.

My solution was to mill a rectangular keyway in the collumn and to provide a captive rectangular key along the lines of the Myford S7 tailstock barrel feature. Clearance is not a problem if you remember to always push the head to the right (or left) on tightening.

The single cone point screw impinging on the Vee shaped slot will over time form conical indentations in the Vee.

Jason's suggestion of a separate mating Key is a good idea, but I would prefer to see two screws, or one screw and two dowels to locate the Key. I would expect the the Key to jam with only one fixing point. Due mainly to the turning moment imposed by the weight of the milling head when the clamp is released.

I did describe an attachment some while back in MEW for the Compact 5. Jamie Wood supplied the photographs. This design was a spin-off of one originally intended for the Unimat 3. Both items used to be sold by Neil Hemingway back in the 1980's. A photograph of this does appear in one of the "World of Model Engineering" books published by MAP. This attachment requires no machining of the Column or the Column clamping member. As a bonus this attachment can also be rotated about the Column which a keyway in the Column will not allow on the conventional lathe set-up.

Regards

Gray,

I have found the photographs of Jamie's attachment.

The Unimat 3 version had the alignment bar on the opposite side and used a different clamping device. Similar in action to that found on an Engineers Scribing Block.

This new computer is taking some getting used to so my apology for the double posting.

Regards

Gray,

Hello:

> A question.

> Is the Unimat 3 clamp on the milling column ...

From what see it is solid aluminium manufactured ~ 1980.

Best,

JHM

Hello:

@Gray:

> ... single cone point screw ...

> ... over time form conical indentations ...

Yes, I'm afraid so.

> ... Jason's suggestion of a separate mating Key ...

It is a good idea but it will probably be expensive to get done properly.

> ... an attachment some while back in MEW ...

Thanks for taking the time to find the photos.

Nice system, never seen it before.

After having a look, I stepped back a bit and had another look at the problem at hand.

My first thought was that this is a rather simple no-big-deal milling table which these days commands funny money prices on ebay and such, but NASA/watchmaker's equipment it is not. 8^°

As it has been pointed out, there are drawbacks to milling the slot, machining the mill head, tightening the screw, etc. all of which are genuine and would like to avoid.

As I looked a bit more at the head I thought that I may be able to work out a solution using a system similar to the one used to tilt the head at an angle without much compromise or expense.

The photo shows the markings used to tilt and fix the head at an angle, each marking representing a 5° variatuion and separated by ~ 2.0mm.

Obviously, finer/more accurate angles need a different method, but this one seems to work for 5° increments in a repeatable and consistent manner.

In the end, as all I want is to be able to repeatedly and consistently be able to put the milling axis on the same spot every time (and overcome Emco designer's lapse) I thought I may be able to use what the head already provides me with.

ie: an always vertical 2.0mm slot at the back of the milling head.

Once tightened, the screw fixing the head in place leaves an open ~2.0mm slot traversed by the tightening bolt.

Because of how this part was machined and save severe damage, it will always travel along an axis parallel to the milling column's own axis with the accuracy imposed by the tightening of the part to the column.

This makes it a reliable reference and very useful toward finding a solution.

A 2.0mm x 4.0mm slot could be easily machined on the column and a 2.0mm strip of hard brass measuring 40.0mm x 15.0 mm could be held in place by the bolt , not tight but not loose either.

The brass strip would always slide inside the slot when the bolt is loose and prevent the head from swinging sideways more than just a bit, bringing it back into register as the bolt is tightened.

This is what it would look like:

Two additional two slots could be machined at 30° to either side, making this arrangement a bit more versatile.

If this can get done, the only thing I have not been able to avoid is the milling of the slot/s which seems like a reasonable compromise.

If the brass strip is properly machined/lubricated, it should not get stuck.

Any and all comments welcome.

Thanks in advance,

JHM

Edited By Julius Henry Marx on 14/11/2022 14:59:31

There is a problem with your clamping arrangement in that you cannot clamp the column and the piece of brass. The slot in the Emco column bracket will distort under clamping. Being wider nearest the column and narrower out by the pinch bolt.

To effectively clamp both is asking a lot and any play in the system will defeat the object of the exercise.

Regards

Gray,

Hello:

> ... cannot clamp the column and the piece of brass.

> Being wider nearest the column and narrower out by the pinch bolt.

Yes, I see what you mean.

> To effectively clamp both ...

The thing is that the brass strip does not need clamping.

It only needs to help register the position of the milling head with respect to the column as the bolt is being tightened.

Would making the brass strip and the slot as wide (or a wee bit less) as the spot where the pinch bolt tightens make a difference?

In than way, the far border of the strip would just *fit* there and not be subject to force when tightening the bolt but would register the position with reasonable accuracy as it is being tightened.

Thanks in advance,

JHM

A possibly outrageous ‘evolution’ of Gray’s guide-bar arrangement …

Would it be worth adding a linear slide-rail instead ?

Over the last few years, these have come down a lot in price.

No point putting an ebay link here, but there are many to choose from.

MichaelG

Any play, no matter how slight will be magnified due to the distance the spindle is away from the column.

Back in the late 1970's and early 80's I went through a whole host of trials to improve the Emco alignment. The best solution that worked is the one I have shown above.

Michael,

A good suggestion as it would remove the need to machine the column. These linear bearings were not so readily available back in the 1970's, well not cheaply that is. Although we did use plenty of them in my Toolmaking days for pick and place units on robotic tooling.

Regards

Gray,

Best bet would be to do away with the round column and replace with a piece of square sillver steel which would mount on teh diagonal using teh cast "vee" mount on the back of the lathe bed.

Then make a new rear half of the "head clamp" with a vee in the back and a separate cap also with a vee in it. That would easily clamp up true each time.

The problem with any flat strip in a keyway is that you need some clearance for the head to move up and down and as the spindle is about 100mm from the round column and clearance will be magnified about 5 times.

I let my subscription lapse when I moved, so cannot check it in the online issues, but I remember reading an article on this subject. IIRC it used a second round bar to locate the column and added a leadscrew and graduated handwheel. Looking at the index I think it will be Rhodes. M. "Milling Head Alignment Guide for the Unimat 3" MEW 124 (April 2007).

Brian G

Edit:  This is the article I remembered, and I found some of the text and a couple of photos published here as a news article

Edited By Brian G on 14/11/2022 18:30:50

That article is on the forum here

Edited By JasonB on 14/11/2022 18:24:30

Yes, that is what I meant with the proposals bij Maurice Rhodes.

The modification to the Emco Compact 5 column from Jamie Wood, shown by Graham Meek, is a bit of the same.

Both are nice solutions with (almost) no modifications to the original Emco parts.

Hello:

@Gray:

> Any play, no matter how slight will be magnified ...

Quite so.

> ... host of trials to improve the Emco alignment.

> ... best solution that worked ...

I'll keep that option in mind if I cannot find something simpler and less costly.

ie: the ~ Ø 12mm / 300mm long vertical bar

@JasonB:

> ... any flat strip in a keyway is that you need some clearance for the head ...

> ... clearance will be magnified about 5 times.

Yes, that is a problem but not as severe as not having a way to register the position back where it was before moving it.

Maybe I could use an arrangement such as the one used to set the angle when the milling head is tilted.

ie: an arrow pointing to a line.

A line maybe 0.5 mm wide could be scribed 1.0mm deep into the column and painted with a suitable colour.

A pointer of sorts would then have to be added to the milling head.

I'd say that this method (pointer meeting line) is just as repeatable as the one used to set the angle when the head is tilted.

After the head is lifted/lowered the bolt would be tightened just enough to keep it from dropping but not enough that it would keep the head from moving if softly knocked to the position indicated by the pointer meeting the line scribed into the column.

Granted, I'd have to look at the back of the milling head but this milling table is very small so it can't be too much trouble.

And even then, I can always scribe the line on the opposite side and avoid the hassle.

If it does not work, I can still try other solutions.

Think it would do?

Thanks in advance,

Best,

JHM

Edited By Julius Henry Marx on 14/11/2022 19:10:09

No! not in terms of any meaningful repeatable accuracy. Respectfully suggest you read the postings above.

Robert Butler

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Thanks for the comment, Gray

Here, borrowed from an ebay listing, is the sort of thing that might suit the Unimat nicely:

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MichaelG.

The markings for setting the head at an angle are really only a rough guide, I certainly never used that to set mine vertical always used a square on the bed against something long in the chuck. So similar on the column would not be very accurate.

If you are just going for markings then the laser and line on the wall will be better as any small error on the wall say 2m away will be many times less at the mill.

Edited By JasonB on 15/11/2022 06:57:48

Hello:

@ChrisLH:

> ... had the same problem on my Dore-Westbury ...

> ... mill a rectangular keyway in the collumn and to provide a captive rectangular key ...

Is this the type of key you are referring to?

Thanks in advance.

Best,

JHM

Edited By Julius Henry Marx on 15/11/2022 09:48:43

Hello:

> ... markings ... ... are really only a rough guide

> ... always used a square on the bed against something long ...

Yes, I can see that.

I'll look over all the posts again and see what I can do about this.

Thanks for your input.

Best,

JHM

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You’re welcome, Ady

MichaelG.