Need some help on engraving please

[Michael Breedlove]

Hobbyist here in Tampa, been doing more engraving lately and noticed a minor issues. I began to notice the engravings were much larger than in the design. As you can see in the attached pics, the actual part does not match the preview, note the center of the 6. It appears the tool is going deeper than it should. I am running and older PRT with a G4 upgrade. The Z axis seems to be dead on whenever I check a move. After I ran the part the zero was still zero. The start location is zero on the tool path. The tool was a 90 degree just as specified on the tool path. Not sure where to go next. Any help would be appreciated.

[jerry_stanek]

Did you check that it is indeed a 90% bit. where are you zeroing from top of material or table.

[Michael Breedlove]

Jerry, it is 90 degrees and I zero to the top of the piece. Strange happenings here.

[steve_g]

Michael…
How or why I’m not sure but it’s clear you’re cutting too deep. Are you using a z-zero plate? If so, any chance that the thickness setting got changed?
How are you getting the funky perimeter? It looks like when bit and toolpath don’t match… You said the bit was a 90°, any chance the toolpath was calculated using a 60°?
SG

[Michael Breedlove]

Thanks Steve, I do not use a plate I slide a piece of paper under the bit. I checked and rechecked everything and the bit called for was 90 degrees and the bit measured accordingly.

[steve_g]

Michael…
Can you attach a screen shot of your vectors with the tool path selected? Like the attached image.
Thanks
SG

[Michael Breedlove]

Steve for some reason my prtsc is not working or I cant figure it out yet. Will keep trying.
Thanks for the help.

[Michael Breedlove]

Steve, here it is,I hope.
Thanks
Mike

[Michael Breedlove]

Steve here is a close up.

[steve_g]

Ok, thanks! That explains the funky perimeter… it’s designed that way!
Is this happening repeatedly? I’m assuming that your unit values are correct for the z-axis… Do you know what they are supposed to be? Do you know how to check them…
SG

[scottp55]

Looks like your cutting deeper in the center, as shown by the different laminates on top. That's the area where your #'s are.
Any chance the material is bowing up, or spoilboard isn't flat? (My first thought).
What's your hold down?
scott

[Michael Breedlove]

Steve attached are my Unit Values. The fine folks at Shopbot have helped me with getting those adjusted in the past, for some reason I thought the Z was suppose to be different than the x and y.

Scott
Great catch, the piece was bowed and that caused part of the problem I think. I keep the spoil board flat. I think there is something still amiss.

I use double sided tape that I get at Lowes as a hold down for signs as it is fast and easy.


Fast and easy are important as I have offered all my friends on Facebook a free sign and even pay the shipping and things have gotten crazy. Free is a great marketing plan! I have made and shipped 70 signs so far. Many of my friends are asking, if not outright begging me to start selling signs as they all need them for their friends and family members,

I am trying to simplify things by going to oak covered ply, giving away solid hardwood signs was getting expensive. I know I need to make a production style hold down fixture to hold the blanks.

Thanks again for all the help.

[steve_g]

Michael…
I’m giving you the link to determine the unit value…
If your tool is a PRT without upgrades, it looks like 1273.2395 on all axis is the correct number. Since your X&Y are ok but not that number all bets are off. If it has the 4G up grade, the X&Y numbers you have are correct but the Z should be 2391.831.
SG
http://www.shopbottools.com/ShopBotDocs/files/SBG%2000171%20Settings%20Unit%20Values%202014%2010 %2029.pdf (http://www.shopbottools.com/ShopBotDocs/files/SBG%2000171%20Settings%20Unit%20Values%202014%2010 %2029.pdf)

[Michael Breedlove]

Steve,
Thanks again, I called Frank at Shopbot and he confirmed that I have the right numbers based on my machine and the motors. I am going to do some more experimenting tonight after work.
Thanks

[srwtlc]

Michael,

Check your cutter, it looks like you have either a flat tip (engraving type) and are using a standard pointed type 90º bit in the file/preview. Is the tip of your cutter broke off/worn down, if it's not a flat tip engraving type? Your actual cut appears to have a flat bottom, whereas your preview doesn't.

[Michael Breedlove]

Scott,
It was a brand new 90 degree bit with a sharp point. I have some of the engraving bits and have them in the tool data base. On this I used a straightforward 90 degree bit. Going to give it another shot tonight.
Thanks for the help!

[oddcoach]

Have you checked that the set screws are tight on the drive gears? Also how old are the gears if they are worn you will get sloppy results.

[Michael Breedlove]

Hey John, the gears are in good shape and pretty tight. Thanks for the response.

[Brady Watson]

There appears to be a discrepancy between the physical bit's included angle (you said new 90° bit from package) and the angle the bit is that you programmed the toolpath with. There are several 'old schoolers' here telling you this...

You have to go back into the tool database and start at the top - and work your way down the properties of that tool with a keen eye. Be 100% sure that the angle is correct in the field for the angle...It's really easy to copy/paste a tool and get distracted without putting in the proper angle for the bit. Take nothing for granted...check it even if you are thinking, "Oh that can't be it."

Also, why aren't you using a Zzero plate? They are cheap to buy and/or easy to make. It will make the quality of your work better. Paper is OK for farting around. If you have a heap of signs to do, ya gotta have a plate.

-B

[Michael Breedlove]

Brady, thank you for the encouragement, plate is installed, took me 20 minutes.