accuracy?

[sixpence]

Eureka!

I have finally made my first cuts. I have cut a square 100mmx120mm but it is exactly 1mm out all round.
The lead screw is 10 tpi, guide rails from igus. Hobbycnc board + motors.
Running acad, sheetcam, and mach2. The angles are perfect 90deg. the bit diameter is set correctly with outside offset.
Where could the problem be?
What should I check first and what sort of accuracy are other people getting?

[ger21]

If you're cutting wood, I like to make a single pass into the wood and measure the width with a caliper, to get an accurate tool size. Also, cut some different size squares and see if they are all out 1mm.

[sixpence]

I have now done what you have suggested. It was not a consistant error and much to my surprise it was not perfectly square! I ajusted the bit diameter to suit and reset the alignment. The error is now consistant 1mm too small all over the machine on the x/y axis. any further suggestions would be appreciated since your last one was so helpful.

[blue_luke]

Hello all, newbie here from Montreal...

Two things.....

Once a machine is constructed, what would be a suggested method of insuring or verifying squareness, precision, repeatability?
In other words, how can I spec a machine just built?

Also for sixpence and any other, how the Igus bearings fare?
I am considering the Igus "Drylin W " guide system.
Any comments?
Thanks, Luc

[sixpence]

Hi Luc
I have encountered no major problems with the igus rails so far exept that they were a bit over kill on specs for my machine. The smaller round rails would have been sufficient

[blue_luke]

Sixpence...
What rail guide systeme did you use and what kind of price?

[ger21]

Are you cutting different sized squares? Cut 50mm squares, 100mm squares, 150mm...
Then, if they are all off by 1mm, I'd guess that possibly your machine is flexing. Try cutting one square conventional (CCW) and one climb cutting (CW). Are they different? If so, it could be the tool flexing.

[blue_luke]

Sixpence...
What igus rail guide system did you use and what kind of price?

[sixpence]

Are you cutting different sized squares? Cut 50mm squares, 100mm squares, 150mm...
Then, if they are all off by 1mm, I'd guess that possibly your machine is flexing. Try cutting one square conventional (CCW) and one climb cutting (CW). Are they different? If so, it could be the tool flexing.
__________________
Yes I am cutting exactly those size squares and they are all out by the same. Pardon my ignorance I am still very new at this could you pls explain those terms to me conventional and climb cutting?
Thanks

[sixpence]

What igus rail guide system did you use and what kind of price?
Hi luke
Drylin WS Q-20 -rails 1220mm x2 =R1542.66
WJS200Qm-01-20-slidesx4 =R386.28

Drylin WS Q-20 -rails 610mm x2 = R771.34
WJS200Qm-01-20-slidesx4 =R386.28

WS-10-305mm railsx2 =R256.20
WJUM-01-10 slides x4 =R201.60

The currancy convesion is at present about 6.60 rand to the dollar

[sixpence]

I looked it up silly of me!
cw- clockwise
ccw counter clockwise

Duh!

[spoiledbrat]

If you are using mach 2, it could be that your encoder steps-per-unit is slightly off.