Unimat milling table - post modification

Yes, that's it

Chris

Hi Jason,

The square column would be a good fix as regards repeatability but you would loose out on the infinite locations that you get with a round column. In being able to rotate the head about the column axis that is. Of course you would have two easily achievable positions at 90 degrees, and one at 180. There would of course be the loss of being able to mount the milling table to the column using the Emco adapter bracket. Unless of course you make a new bracket as well.

Generally,

Any solution that moves the location point away from the outside diameter of the column, (28 mm or 14 mm R), is going to improve the accuracy. There is a lever ratio of approximately 5:1 present with respect of the vertical spindle centreline to the centreline of the column. Only 0.01 mm of play in any keyway will equate to 0.05 mm movement at the spindle. The less clearance or play present will make the head harder to move up and down.

The slot will without doubt fill with debris, which will soon put paid to any fine tolerances.

If I was looking to repeat my VAD, (Vertical Alignment Device), today I would go down the linear bearing route. Probably a sealed ball bushing and plain hardened shaft, but using the two VAD brackets. This will never wear out and once fitted not give any further trouble.

Regards

Gray,

Edited By Graham Meek on 15/11/2022 12:05:25

Hello:

@Chris:

> Yes, that's it

Right.

I found an exploded diagramme of the tailstock to see the rest of the parts, I cleaned it up a bit for clarity.

Am I correct in assuming that the key is *first* put in place inside the tailstock and then the rest of the barrel assembly is set in place?

Edit: I just now saw your PM, had not received a notification.

I'd appreciate if you could make some time to post a photo/sketch of how you implemented this in the column of your Dore-Westbury mill.

Also, I don't quite understand this:

"Clearance is not a problem if you remember to always push the head to the right (or left) on tightening ..."

Thanks in advance.

Best,

JHM

Edited By Julius Henry Marx on 15/11/2022 12:10:24

Answering the sketch etc. will take a little time but, looking at the D-W machine, it's a bit more complicated than I suggested because, due to the need to lift the considerable weight of the head, there is a coarse screw thread machined in the collumn and a "nut" to engage it.

Regarding "Clearance .....", I was assuming that there is no requirement to raise or lower the machine head whilst cutting drilling, etc. i.e. the head is clamped whenever cutting is taking place. So, although there may be considerable slop between keyway and key, as long as the key is engaging the same side of the keyway every time the clamp is activated, alignment will be maintained. This assumes,of course, that the keyway is machined parallel to the axis of the collumn, etc.

Hello:

> ... the sketch etc. will take a little time ...

Don't worry.

I can probably manage as it is just a column and the clamp. (see photos in posts)

> ... assuming that there is no requirement to raise or lower the machine head whilst ...

Quite right, no such requirement.

Actually, the head cannot be moved while milling, at least in its original OEM configuration.

The quill does have a lever-type arrangement with ~ 25mm travel which enables it to be used as a drill press.

To move the quill downwards while milling, a fine-feed attachment with a dial and a worm gear is used.

It works in conjunction with the lever action gear, allowing a bit over 0.10mm (four thousands) downward travel per each turn of the dial, with the same ~25mm travel.

> ... as long as the key is engaging the same side of the keyway ...

> ... alignment will be maintained.

Right, I see it now.

Thank you very much for your input.

Best,

JHM

Edited By Julius Henry Marx on 15/11/2022 16:19:32

Hello Julius,

I've just mugged up on posting photos so just for fun I'll complete the exercise. Top picture shows the raising arrangement in its normal state. The top disc with tommy bar holes is the "nut" The thinner disc below it is the "key". In the bottom photo the "nut" has been wound up the collum to give an end view of the Myford type key which engages the coarse screwthread. The "key" which engages the vertical keyway (which is just visible on the RH Side) is just a thick plate profiled with a tab projecting inwards from the bore. The "key" is normally prevented from rotating by a short dowel into the casting below. The dowel can be removed should the need arise to rotate the collumn.

Hello:

> ... so just for fun I'll complete the exercise.

Yes, it took me a while to figure out how to post photos.

So thank you for taking the time to do this. 8^)

I expect that it will be much simpler to get this done on my Unimat's column.

The real trick will be to make the key (a smallish thing), almost exactly like the one used on the Myford and fortunately not as small.

Once again, thank you for your input.

Best,

JHM