Warco mini mill cnc conversion

Hi,

I have a warco mini mill which has recently been converted to CNC using cncfusion kit 4.
The machine works great with backlash <= 0.03mm and smooth table travel. But, I have a major problem.

When the machine was being used manually I never checked the squareness of the X and Y axis.
But now with the resulting resolution of the CNC I have noticed a major flaw:

1) When I machined a large circle (50mm plus) the resulting circle was not round. This is a classic backlash problem but proved to be not the case.
2) I machined an 'L' shape edge (200 by 70mm) into 3mm plastic and the resulting square edge was out by about 0.3mm on its longest side.
3) Because of the above I decided to measure the squareness of the X and Y axis using the following method:
a) Squared up a 400mm length of straight edge (25mm by 10mm profile +- 0.01mm over 300mm) along the X held in a vice.
My best effort achieved +- 0.03mm repeatability over 300mm which meant the X table travel was ok.
b) Made sure the vice was solid and replaced the bar with an engineers 150mm square held in the vice.
c) I now measured the Y axis movement along the right angle formed by the square. The results were alarming.
Over only 75mm in the Y direction the error was 0.32mm which means the Y axis was running at an angle to the X axis. This is hard to believe especially when the X and Y are running so smoothly under CNC control.

I repeated the above measurements by setting up to the Y axis first and then checking the squareness of the X . Same error found.

Any ideas how to resolve this problem.
Thanks

This one?

http://www.warco.co.uk/productimages...n_004850RB.jpg

The question is how the table attaches to the Y-axis. On my bigger one the table is machined with integral dovetails that run on ways machined in the Y-saddle, similar to this one of an X2 If so its hard to see how they could get misaligned. All the pictures I can find of the mini-mill (X2 clone) seem to suggest its much the same unless the saddle is in two parts? Are the gibs tightened up? A loose gib could allow the table to twist on the saddle, or the saddle to twist on the y-ways.

Attachment 1678

Thats' the one.
The X/Y saddle has dovetails machined presumably!! at 90 degrees same as the X2.
I am trying very hard to see how the X and Y can be out of square, it's also very difficult to do an actual
measurement of the complementary dovetails on the saddle to check their squareness.

The gibs were nice and tight and threadlocked and the steppers had an easy life moving the table (3Nm) . Table also had
no more than 0.08mm play with the X extended to far right/left.

I should of noticed this problem about 10 months ago.

when you did the test did you lock the gibs on the stationary axis?

The other thing i would do is put the base of the engineers square in the vice but proud of the top and indicate along that in the X to make sure its still aligned that way - it should be. with the Y-gib locked. Then move to the other leg of the square, lock X and release y and then indicate Y. that way you haven't got any disassembly between tests... or do the same things with a 123 block on the 3+2 sides.

If the ways are not machined square I suppose it would be possible to have them recut and fit a wider gib-strip (if need be). You could remove the table then indicate the Y axis movement relative to a square clamped to the x-way... that would give a clue as to which way is mis-aligned

I visited the garage about 45 mins ago to recheck everything again and
it's true the Y is not square to the X and again I got >0.3mm over about 60mm along the engineers square. I even checked the engineers square and its fine.

Tomorrow I will try you idea of indicating the Y movement relative to the X.

Let you know the result.

I did another test tonight with the table removed and checked with a square
how true the Y movement was. The results show a 0.4mm error over about 65mm.

I repeated yesterdays test and set the dial to +-0.03 over 140mm on the X axis. A 6inch square held in the vice as before and I get 0.62mm error over a Y movement of 120mm. From this I can work out the angle error between the saddle X and Y dovetails.

I now have two choices, either get someone to machine the X/Y channels true
or possibly get software to compensate. Can mach3 auto compensate for non true XY axis!!!

I would strip the table and saddle off to check there's not swarf or other crap trapped in the dovetails. I would not expect these little machines to have tapered gibs, so any foreign body on the fixed side could cause the problem with giving a tell-tail loose gib on the other.

Bill

BillTodd,
I just removed the saddle and examined the LHS dovetails and indeed the machining was not good. At the top of the dovetail was a small (0.1mm) of unmachined
ramp shaped metal 2/3 thirds the length of the channel. I scraped most of it away with a thin file and finished with off with 600 grit.
If I keep up this scraping process I will of course do two things - ruin the dovetail or get no near perfection!!!

I will reassemble the lot tomorrow and retry the previous laborious calibration setup again.

I have reduced the XY error to 0.4mm max over a Y travel of 98mm but the LHS Y dovetail has now in my opinion been scraped too much. So anyone know of a reasonably cheap!
engineering firm in Bedford or surrounding area capable of machining this mini mill saddle.

I might consider travelling up to 50 miles to get it done,
Thanks for all your help.

I had the saddle machined by a local company. They first measured the dovetails for parallelism and the results was not good. The fixed end was out by 0.43mm and the gib side was out by 1.05mm.
Both end were machined with a 30 degree dovetail and the results are truely wonderful.

On the machine I now get 0.03mm worst case after lapping the gib on the y axis and making slots for the set screws. In addition I replaced all the 0.125mm balls in the ballscrews with 0.1268mm and this has achieved 0.08 backlash.

I thank you all for the helpfull replies. :smile:

Who did it and how much did they charge?

http://www.constant-precision.co.uk/ based in Kempston Bedford. They did it in less than 2 hrs and charged 30 pounds.

wow... well bedford's only a short drive up the motorway from me. I don't know if mines that bad - need to measure it. but before i do the CNC'ing work, while its all in bits I may get that sorted if need be. Mines a tad bigger and heavier...

There does seem to be a problem with the Warco Mini mill. I have just recently bought one and the X Y axis are not at 90 degrees. I too will have to get mine machined. The error I measured was 0.25mm over 100 mm on the Y axis. This is a pain to have to correct on a brand new machine. It came with a test certificate that stated it was measured at 0.025mm over 150mm. Clearly the machine was not measured.

John

Quote:

---

Originally Posted by John Wright

There does seem to be a problem with the Warco Mini mill. I have just recently bought one and the X Y axis are not at 90 degrees. I too will have to get mine machined. The error I measured was 0.25mm over 100 mm on the Y axis. This is a pain to have to correct on a brand new machine. It came with a test certificate that stated it was measured at 0.025mm over 150mm. Clearly the machine was not measured.

John

---

Or not measured correctly... If its a new machine and clearly out of spec then I'd return it under Sale of Goods Act 1974 as 'not fit for purpose'. If it was bought 2nd hand then you don't have much option, but check first that there's no swarf etc trapped in the slides.

I am pretty sure I have measured carefully. I measured after cleaning all grease off the mill and the ways. I redid the measurement several times as well as checking the other specs on the test certificate. They were all ok, it was just the XY that was out. The reason I bought the mill was for conversion to cnc. I need the extra movement of the Y axis that this mill offers over the normal Sieg mill. If I was to send it back and get a replacement then I may well get the same problem. From my point of view it is simpler just to get it fixed and know it is accurate.

Interesting issue about the Y axis movement. They advertise it as 130mm. However if I measure the movement from the centre of the table it is 55 mm to one side and 85mm to the other! Strictly speaking I guess that it is only a 110 mm table movement unless I add a 15 mm spacer block to the head, which I could easily do. This would give me 140mm. I could also make an extra aluminium table if I want that would project more to the rear than the front by 15mm. There is room to move it back.

John

Just got back from having my X Y dovetails on the saddle re-machined. The error in the Y axis was indeed 0.25mm over 100 mm. The machining done originally was terrible and looked like a ploughed field. All looks much better now, and I was able to watch as the part was clocked up and machined.

John

Was this at the same place as Buster had his done?

Yes it was, very friendly and helpful.

John

Hmmm... maybe we should get a group buy going...lol

How much of the mill did you take over to them? Mines a 2-man lift in and out of the car (just the base weighs ~150kg).

Hello Buster,
Ive just stumbled across the same problem with my mini mill and found it extreamly interesting reading your thread. After machining a 100 mm 'square' sheet of aluminium and checking it for square I found my mill was .2mm out of true and like yourself assumed the dovetails on the saddle are machined out of square to each other. can you please inform me as to the engineering company you used to have the saddle re machined as I live not too far from Bedford.
Thankyou
steve

Hi Steve

I used Constant Precision, the same machine shop that Buster did in Bedford. They still had the mill set up for his machining and did it while I waited. They were very reasonable and helpful.

http://www.constant-precision.co.uk/

It was such a nuisance that the dovetails had been machined so innacurately, but the cure was quick after I removed the saddle. I discovered my problems before I fitted the ballscrews as I saw a thread about innacuracy with the mill.

Now it has been done I get very good results and have used the mill for several jobs since then.

This video will show you one of the tests I did. I know it is painfully slow machining, but of course I have faster speeds set since then.

http://www.youtube.com/watch?v=qRpMx-qp5ik

John

Hello John, Many thanks for letting me know about Constant Precision and I will certainly give them a call and hopefully they will re-machine my saddle too. Im very glad you got your mill sorted out in the end and I suppose there is a moral in this story for us that you only get what you pay for however it seems that once this re machining is done the mill is then perfectly accurate.I will keep you informed how I get on,once again many thanks for replying to my question.
steve