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Re: Non circular holes and lack of precision?

Posted: Wed May 14, 2014 9:04 am
by morten_denmark
Hi

My number 1 concern was non circular holes.

This is what i have done so far:

I bought a 4x40x1000 piece stainless steel bar to be sandwich in-between the two x-axis maker slide.
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The modification help, but only very little. I guess that the rest of the deflection i in he V-wheels on the X-axis.
But i have tried to tighten them more, with no success.

Next step is to do some more/better work, on making my shapeoko square and plumb.

As i can see the problem occurs in the spot, where the bit make the plunge.

Re: Non circular holes and lack of precision?

Posted: Wed May 14, 2014 12:54 pm
by twforeman
putting a flat bar in the middle will help a little, but it won't add a lot of rigidity.

I'm going to bolt a piece of angle to the inside of my makerslide, that should stiffen it up a bit.

Re: Non circular holes and lack of precision?

Posted: Wed May 14, 2014 2:09 pm
by Nigel K Tolley
To gain anything there, you'll need to tighten the screws rather a lot to get the clamping force high enough to make any difference to stop them sliding and twisting.

Perhaps if you bond them with superglue?

That's semi reversible as you can kill it with a heatgun or superglue remover, but will stop the 3 pieces from sliding.

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Re: Non circular holes and lack of precision?

Posted: Wed May 14, 2014 6:17 pm
by McOtis
I remember when milling hold down holes for my waste board, the direction of cutting made a big difference in the roundness and size. My bit was bending much more depending when I climbed or conventional cut - AKA clockwise or counter inside of MakerCAM.
Or was I imagining things due to being a complete newbie at the time? :-)

Re: Non circular holes and lack of precision?

Posted: Wed May 14, 2014 6:19 pm
by WillAdams
On a lightweight machine which isn't too rigid, direction of cut makes a big difference --- unfortunately, there's no way to take advantage of that for a simple drill operation.

Re: Non circular holes and lack of precision?

Posted: Wed May 14, 2014 8:08 pm
by twforeman
McOtis wrote:I remember when milling hold down holes for my waste board, the direction of cutting made a big difference in the roundness and size. My bit was bending much more depending when I climbed or conventional cut - AKA clockwise or counter inside of MakerCAM.
Or was I imagining things due to being a complete newbie at the time? :-)
You were not imagining anything. Unless your machine is very rigid (the ShapeOko is not) you should always do conventional cutting.

I tried some climb cutting in maple and it was not a success.

There is some discussion here: http://www.shapeoko.com/forum/viewtopic.php?f=7&t=3375

Re: Non circular holes and lack of precision?

Posted: Thu May 15, 2014 8:35 pm
by morten_denmark
all my milling was done conventional, i did try climb... much worse!

Today i used a dial indicator, so we could get some numbers on the deflection :)

1. I think that the steel bar, between the two pieces of Makerslide did make it more rigid.
I measured the deflection on the X-axis Makerslide to be 0.1 mm

2. Measuring on the spindle, there was a bit more 0.3 mm. What is acceptable?
Here is a link to a video:

https://dl.dropboxusercontent.com/u/23750303/ur.MOV

3. Just before i went home from the workshop, i did a last try to locate the problem,
It tried to push the bit to the sides instead of back and forth (don't know why i didn't do that before).
I could see, the deflection on the sides to be worse.
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I just ordered some extra V-wheel, to add on the Z-axis and see if it helps

Re: Non circular holes and lack of precision?

Posted: Thu May 15, 2014 9:09 pm
by Nigel K Tolley
WillAdams wrote:On a lightweight machine which isn't too rigid, direction of cut makes a big difference --- unfortunately, there's no way to take advantage of that for a simple drill operation.
I recommend using clockwise rotation for hole drilling. ;-)

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