PRECISION QUESTION

[chodges]

I am not (yet) a ShopBot owner, but I am trying to research as much as I can before committing to a specific machine.

I want to use a CNC router for both cutting out parts and for engraving into substrates. I have been told that rack & pinion machines have too much slop to achieve the positional accuracy needed for engraving small (1/4" or so) lettering, and that I should be looking at a machine with a single lead screw instead.

Can anybody please comment on this from your experience with using a ShopBot for precision engraving?

Thanks!

[myxpykalix]

I have a different machine that is a legacy ornamental mill that is based on a "lead screw" design and it is the sloppiest design for a machine i've seen. The mfg even tells you to overshoot your end and back to the beginning by 1/2" and realign because of the slop built into the system.
With the shopbot its built with tolerences that don't allow for "slop". I don't use mine as a production machine everyday but it is as tight and precise today as it was when i bought it a yr and half ago.
Go to the "signmaking" section and talk to some of the guys about their experiences with small lettering. I think you will find an overall satisfaction with the quality they get from their bots.
Sharp good quality bits will be a major factor also and for that talk to fred at www.centuriontools.com (http://www.centuriontools.com)

[jsfrost]

I have not yet pushed for smaller, but I have cut many sucessful projects with V carved 1/4 inch letters. But don't take my word for it. Try to arrange a demo with an owner in your area and check out the accuracy for yourself.

[Brady Watson]

These were the 1st engravings that I ever did on the machine several years back. Regular old AL sheet and an engraving bit. Pictures are from my then lousy 2.0 MegaPixel camera, so they really don't show as much detail as they should. These were cut on a 2001 PRT with 1/4 stepping drivers. The new PRS Standard will run circles around what this machine can do in both speed and resolution by a factor of 2.5 times. My PRS Alpha machine will run circles around the new PRS Standard...The precision is there with the rack and pinion. Anyone who tells you otherwise is mis-informed. If you are looking to do jewelry and things like that, then you shouldn't be looking at big router - get a small machine with ballscrews and dovetail ways. If you are only looking to do occasional engraving, then you'll be fine with a ShopBot.


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-B

[ed_lysne]

I've have a benchtop alpha and I'm still learning. 1/4 lettering with the right bits and material should not be a problem. I do guitar work and biggest issue for me is really small work. I use a router and with bits in the .0230 and smaller range there is just too much run-out in the router. My router has ~.003 run-out... and everyday I wish I had a spindle. I cut shell and wood material and have not problems with movement accuracy... but I sometimes break small bits due to slop in the router.

[wayneo]

Hey Brady,
Great looking engraving! Care to enlighten us with the particulars about the bit? Size, feed & speed? What was the depth? Have you ever tried this in any kind of plastic?

-W

[drodda]

Wayne,

http://www.talkshopbot.com/forum/messages/29/6550.html
This was the original post that we discussed the examples that Brady has shown.

[Brady Watson]

Thanks guys. Just chuck a bit in, put your safety glasses on and observe what is going on. It will tell you if you need to speed it up or slow it down.

-B