[Rickyg]

So first.
I get why everyone likes CNC routers.
I cut my first part this weekend and it was cool. My mind races with the things I would like to build that never could before building this machine.

But I ran into something odd, I snapped a bit while making my first attempt. I am guessing wrong type of bit or to fast not sure. Thats not the issue.
I attempted a restart after changing the bit. But I guess I didn't do it right so I messed it up. not a biggy, I knew going into this I would screw up more then I was successful at in the beginning.

so I started over. New bit all was good. Cut perfectly. With one small exception.
The whole part was 1/16th smaller on all dimensions then it should be.
I cut a second part that was drawn from this first part. Basically two pieces going back to back. But the one part is easily 1/16 smaller. I thought it was the bit and checked its dimensions. Thinking it to have slightly wider flukes.
Nope same diameter.

In the end its not a problem for what I built. but with no explanation I am concerned the next time it will be a bigger issue.

hmm..could a missed step or two do this.

I was cutting MDF with a 1/8th bit and mdf is mean stuff.

Just curious.

[awerby]

This doesn't sound like lost steps, which are usually more random. It could be tool deflection, or mechanical slippage of some sort. Try running a few simple identical parts and compare your results. If the result is consistent but wrong, it might be deflection, backlash, or your steps/unit settings being slightly off. If it's inconsistent and wrong, then it's more likely to be lost steps or slippage.

Andrew Werby
www.computersculpture.com

[Rickyg]

hi and thanks.
I did as you suggested, I created 4 identical parts. A simple drill function and an outline function. All cut perfectly.

so I am thinking defection. I snapped a bit once doing the same cut so I am pondering the possibility of a feed rate issue. Running it to fast causing deflection and subsequently the error. MDF is tough stuff.

So assuming its a deflection issue or a feedrate/deflection issue I need to do some research.

I am reading up about bits. I was using HSS and it seems I need Carbide for MDF.

Also I think I can see some flex in my Z axis, so now that I have a working CNC device. I can build parts to upgrade my Router. Wa hoooo.
got to love this technology.

[dsnaith]

hi and thanks.
I did as you suggested, I created 4 identical parts. A simple drill function and an outline function. All cut perfectly.

so I am thinking defection. I snapped a bit once doing the same cut so I am pondering the possibility of a feed rate issue. Running it to fast causing deflection and subsequently the error. MDF is tough stuff.

So assuming its a deflection issue or a feedrate/deflection issue I need to do some research.

I am reading up about bits. I was using HSS and it seems I need Carbide for MDF.

Also I think I can see some flex in my Z axis, so now that I have a working CNC device. I can build parts to upgrade my Router. Wa hoooo.
got to love this technology.

You may want to check the runout on you router collets.

[Rickyg]

Sorry not sure what your referring to.
However if I took a guess, I am going to assume your suggesting play in the collet that allows for the bit to move off center. If this is the case, I have no clue how to test that. But will go and read some more.

thanks

[dsnaith]

Sorry not sure what your referring to.
However if I took a guess, I am going to assume your suggesting play in the collet that allows for the bit to move off center. If this is the case, I have no clue how to test that. But will go and read some more.

thanks

it is not necessarily play so to speak. It is a lack of concentricity, that is, the distance between the axis of the cutting tool, and the axis of rotation of your spindle. You can check it with a dial indicator fixed to your table and indicating the shank of your cutter. There should be no displacement of the dial as you rotate the tool by hand. If you have run out, you can compensate somewhat by increasing the theoretical tool diameter in your cam programme.

Dave.