Problem With Cutting Fonts

[sawdust535]

When V-Carving fonts, especially 1/4" or less lettering, I'm not getting a clean cut. If you can see in the photo, the lettering is wavy and the V-Bit seems to be entering even a small area multiple times, like in the dot over the "i" (looks like the bit entered it four times when one should have been enough" The lettering was about 20 points (1/4" high). Also, when I am cutting fonts with a 1/8" 2-flute bit, I am getting ridges that hopefully you can see in the second photo. The depth of cut was 5/8" at 1/8" passes using poplar. I purpusly took 1/8" multi passes to see if the ridges were in the same spot throught the thickness of the material, which they were. Whats interesting is in the same part file, I cut other curves, and a circle that cut perfectly. Not have any trouble cutting even the smallest non-font shapes, including curves and circles using the same bit and similar cutting parameters. Just seem to be have a problem with fonts. Using true type fonts in Corel Draw, exporting to PartWorks as an EPS file as curves. The V-bit parameters for the small type are: 60 deg 1/2" V-Bit, .0065 (1.3%) Final, 0.1 (20%) Clearance, 13k rpm, 2.0 Feed Rate, 0.5 Plunge . . . . .
The End Mill parameters for the small type are: 1/8" 2-flute end mill set to climb cut, 0.125 Pass Depth, .05 (40%) Step Over, 14k rpm, 2.0 Feed Rate, 0.5 Plunge . . . . .
Any help would be much appreciated

3860

[sawdust535]

Here is the second photo using a 1/8" end mill . . .

3861

[Brady Watson]

Speeds are WAAAAAY too fast! You need to slow things way down when cutting details that small. The deviation in cutting path is attributed to slop in your machine, and reverberations from speeds being too high getting transferred to the cut. Grab the Z axis and wiggle it all over the place. If you hear any 'ticking' or feel any movement, you need to adjust the v-roller bearing eccentric nuts to ticghten things up.

Go to ShopBot's homepage & look at my article under 'Brady's Tricks' about the VR command, specifically the area that talks about XY Ramp Speed. Your move speed should be in the 0.2 IPS range for XY, when cutting these small engravings. If your XY Ramp Speed value is set at the default .4 IPS setting, then the tool will never cut at a speed below that. I would set it at either .1 or .2 for these types of jobs ONLY. Use the US command to save a config for 'SmallEngraving'.

You MUST download the latest control software, 3.5.7, if you want to have good results at these lower speeds.

Your 2nd pic is attributed to slop in the pinion gears, IF you are running a newer machine. This may or may not be 'normal' on an older PRT. Your pinions are either worn (most likely) or if a PRS, pinions not fully engaged. If your rack is dry, your pinions are smoked. Order up a new set & grease racks with the grease SB gives you.

-B

[sawdust535]

Brady, the machine is a new BT32 Alpha model. I checked the Z axis and it appears to be tight with no play at all. The racks are greased, I'll apply more but the machine has low mileage on it and they seem well greased as they were from the factory. I'll try the other suggestions, including slowing down the move speeds. I hope its not a problem with the pinions (they seem to be fully engaged). What I don't understand is if I cut an inside or outside circle the same diameter as the letters in that photo,and same speed, I get a perfectly clean cut. It seems to only happen when cutting text. I cut some very small pieces last week with several 1/4" inside radius with no problems.
The other strange thing is what I mentioned in the last post . . .
[The depth of cut was 5/8" at 1/8" passes using poplar. I purpously took 1/8" multi passes to see if the ridges were in the same spot throught the thickness of the material, which they were.]
If the pinions were loose or damaged, wouln't the ridges be at random places for each pass depth?

[Brady Watson]

George,
Post or email me your PartWorks file for the poplar cut out. Your vectors could actually have those marks in them.

-B

[bill.young]

Hey George,

I don't use Corel but wonder if the fonts are being converted to segmented polylines when they are exported. A quick way to check if it's a problem with the file or with the cutting is to run the file in Preview mode, zoom in, and see if the Preview looks the same as the cut part. If they are the same then it's a file problem...if not then look for cutting problems.

Bill

[sawdust535]

Bill
I just checked the preview and it looks fine. Thanks for suggesting that. I thought maybe the EPS file was exporting improperly, but zoominig on the tool path rules that out.
BTW, when greasing the rack, do you also apply grease to the area where the V-rollers ride on, or just the teeth?

[Brady Watson]

Only the teeth...unless you want a real mess!

You have mail.

-B

[sawdust535]

Brady

You were absolutely right about the ramping.
I read your article on VR Settings and now understand the importance of these settings.
I sent you an e-mail to describe my changes and results.
Again, thanks so much for your help.
George

[Brady Watson]

Glad it worked out. There are some additional commands in the VU settings that now allow for slower cutting speeds.

-B