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Milling Table "fault"

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Roger Williams 203/08/2018 16:38:10
338 forum posts
1 photos

Hello all, on my milling machine, an Emco F1P, I have found which I presume is not right, nearly 0.010 inches discrepancy over 5 inches of travel on the Y axis. The parallel I am using is perfect, there is no lift in the table and is fine on the X axis travel. Not knowing a great deal about mills, I am guessing that the top surface of the table isnt parallel with the bottom across ways so to speak . Oh, and the top surface of the table is unmarked.2018_0803_03114400.jpg

I would be grateful for anyones help. Many thanks.

Neil Wyatt03/08/2018 16:45:47
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18807 forum posts
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I'm always suspicious with indicators mounted on long arms like that,. can you mount it directly (or more nearly directly) in the spindle. Also reverse the parallel and try again, just in case.

Neil

Pete Rimmer03/08/2018 16:54:57
1096 forum posts
69 photos

It's far more likely to be the column that's out of perpendicular to the y-axis ways. Does the column bolt to the base?

Roger Williams 203/08/2018 17:25:37
338 forum posts
1 photos

Neil and Pete, yes I will try out your suggestions. I have thought about the column being out ( it is bolted ), but cant see how it would make any difference, however, I will definitely try it . Hope Im proved wrong !!. Many thanks.

Tony Pratt 103/08/2018 17:57:33
1757 forum posts
8 photos

If you are traversing the y axis under an indicator the column being 'out' or not will make no difference.

Tony

SillyOldDuffer03/08/2018 18:29:28
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7690 forum posts
1697 photos

I've noticed quite a few reports of mills and pillar drills having a slight forward nod. Is it possible on the lighter machines that it's deliberate in that the column is designed to straighten out when cutting pressure is applied? My cheap pillar drill has a distinct forward lean, but it still drills vertical holes. Sticking a DTI on it shows it straightens up when pressure is applied to the drill.

Making a machine completely rigid is hard. Compensating for bending in use might be a clever way of keeping costs down. Obviously the result will be inferior to a truly stiff construction, but perhaps it's acceptable considering the reduced cost.

Dave

Pete Rimmer03/08/2018 19:01:58
1096 forum posts
69 photos
Posted by Tony Pratt 1 on 03/08/2018 17:57:33:

If you are traversing the y axis under an indicator the column being 'out' or not will make no difference.

Tony

Tony you're quite right, I had a senior moment there. I'll blame it on the heat, or the hard day at work etc.

Gas_mantle.03/08/2018 19:10:52
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359 forum posts
269 photos

Do you get a similar reading across the table when measuring at each end ?

Roger Williams 203/08/2018 22:39:45
338 forum posts
1 photos

Gas mantle, yes I do. The parallel itself is accurate to a couple of tenths over its length and the Noga DTI set up is rigid. Ive had the mill for about 10 years , this being the first time Ive noticed this error. The reason Im checking now is because a milling vice (5 inch width ) I machined 2 years ago, checks perfectly along its length, but 10 thou out across its width, the length clamped to the table on the X axis during the job.

Im beginning to think that the mill was sold because of this fault.Im convinced just about , that the table will need regrinding. Oh bother !.

Edited By Roger Williams 2 on 03/08/2018 22:43:28

duncan webster03/08/2018 22:58:09
3589 forum posts
66 photos

Can you masure the thickness of the table from top to bottom sliding surface front and back. If the 2 measurements are the same then I think the fault must lie elsewhere

Paul Lousick03/08/2018 23:08:51
1868 forum posts
666 photos

Hi Roger,

"I've noticed quite a few reports of mills and pillar drills having a slight forward nod. Is it possible on the lighter machines that it's deliberate in that the column is designed to straighten out when cutting pressure is applied?"

To check if this is the case, machine a test piece and check to see if it is thicker at one end. If the column is bolted to the base, you can shim one side to make it vertical. Also do a Google search about fixing your mill problem. Lots of examples on the net.

Paul.

 

Edited By Paul Lousick on 03/08/2018 23:11:43

I.M. OUTAHERE03/08/2018 23:59:44
1468 forum posts
3 photos

Do you have the X axis locks applied ! If not try it and if the problem dissapears or lessens your table may be bowed on one side .

The next step is to determine where the problem lies , is it the table and / or the X axis slideway out of kilter or is the Y axis slideway the issue ?

If the table is just a bad grind - thicker on one side than the other you could get it re ground at a reasonable cost .

I have heard of some machinist doing a fix themselves by using a face mill to re machine the top of the table .

Roger Williams 204/08/2018 08:32:26
338 forum posts
1 photos

Duncan, Paul and XD351 ; as you are all saying, Ive got to measure the thickness of the mill table for a start and then the table underneath too if necessary. Im getting the same error all the way along the mill table. Im going to remove the table and put the parallel on the table below it and measure that, the Y axis, if that makes sense. It seems that one of them needs regrinding. So much for Austrian quality control. Thanks toi all.

SillyOldDuffer04/08/2018 09:53:32
Moderator
7690 forum posts
1697 photos

Before tearing the machine apart Richard, have you confirmed that the lean causes a problem in practice? Although you're probably right, it's remarkably easy to be led astray by when testing machines, and also easy to misdiagnose causes. If it ain't broke, don't fix it.

Also, if you haven't already done so, check everything. For example, does the DTI in your test set-up register any movement when you push the column?

It may be you have a wrongly ground table from new, but that seems unlikely. It could be due to wear, but the table top being clean suggests otherwise. Unless, that is, the top was reground badly in the past by a dodgy salesman to make it look good! Most likely, I feel, is that the column/head has moved in transit and you may be able to fix it by shimming.

I think it's worth spending some time checking work made by the mill, and also taking more measurements to pin down the cause. Apologies for wasting your time if you've already done all that!

Dave

anthony smith 404/08/2018 09:53:35
10 forum posts

HI ROGER LOOKING AT YOUR PHOTO OF MILL THE HEAD IS TILTING TO FRONT OF THE MACHINE I WOULD SHIM THE FRONT OF THE COLUMN WITH A FOUR THOU SHIM MOUNT THE DTI IN THE CHUCK

AND CHECK AGAIN THIS WILL TELL YOU IF YOU HAVE TO INCREASE THE SHIM OR SHIM THE REAR OF THE COLUMN CASTING

Paul Lousick04/08/2018 10:43:46
1868 forum posts
666 photos

Roger,

If the discrepancy is similar for the whole length of the table, it is probable that the column is not perpendicular to the base. Either the mounting pad or the base of the column has not been machined square. It is easily fixed by smimming one side of the column base to make it vertical. This will require a bit of trtial and error to achieve the correct thickness of shim material. If you do not have the exact thickness of shim for packing one side only, you may have to pack both sides with differen thicknesses to achieve the desired thickness between front and back.

This is not an uncommon problem with lots of examples published on the internet.

Paul.

Hopper04/08/2018 10:57:13
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5505 forum posts
137 photos

Could it be a bit of swarf, packing gunk, paint, burr or the like on the dovetail slides under the table, or under the X axis slideways?

Is this a new machine? Has it been used at all? Did it machine square if so?

Nick Hughes04/08/2018 11:01:07
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256 forum posts
143 photos

If the OP was holding the DTI in the spindle and then rotating the spindle by hand, then the error would be the column, but as he is not and just moving the Y Axis then the error is in the table.

0.010" is nothing to worry about IF you're happy producing wedge, or parallelogram shaped parts. However if you want to produce accurate, square work then it needs correcting (and THEN also check the Column alignment, shimming if needed)

Nick.

Mike Poole04/08/2018 11:23:19
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Moderator
3095 forum posts
72 photos

Providing the column and indicator are rigid and you are seeing the error when you wind the table in and out then I would strip the X and Y axis and check there is no foreign bodies or dirt or damage to the slides. After a good clean and inspection reassemble the first layer and check that the table guides are true, if they are ok the refit the table and check all the gib strips are in the right way as they can lift a slide if they are the wrong way up. While it is all apart and clean it should be easy to take some measurements to establish that the parts are machined correctly. I would find it surprising if the parts are badly machined and you are probably going to find a foreign body or an assembly error.

Mike

Emgee04/08/2018 11:53:38
2195 forum posts
272 photos

Hi Roger

I'm surprised that if using the mill for 10 years you haven't noticed thickness differences back to front on parts made during that period, it does seem that either the Y axis base slideway is not ground on the correct plane or the table surface is not parallel to the slldeway, either way for accurate parts you need to rectify the problem.

Emgee

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