Baffling Bit Diameter

Good afternoon all,
I am having a problem. There should be a simple solution, but I am obviously missing it.
Here is the project.

The material is basswood, a relatively soft wood and easy to machine.
The project is cutting a simple outline. I am using a 0.250" spiral upcut but. The first run (Rough) is intended to remove most of the material. I defined the bit as a 0.270" diameter because I wanted the bit to cut a little farther away than the finished dimension. The the second run (Finish) is done with the same bit, same zero points, but defined as a 0.250 bit (have also tried 0.240 bit), but run at full depth in a single pass. The idea is to shave the edge so I have a nice smooth finish all around. But I am not getting that. I still get a ridge. Any suggestions?

instead of tricking the toolpath with bit size you could use the offset tool to make an offset (outward) as a second workpiece and carve that one first (using the correct bit size) and then carve the correct size one also using the right size tool.

Regarding your fray there, it looks like your using an upcut bit an may have need to tram. Is that fray on all 4 sides? (top, bottom, left and right) if its only 2m that’s a sign the tram is off.

OH and Easel tends to run a conventional cut type which does not do well to achieve a side wall finishing pass like you are trying to do, not to mention the X-Carve is not the most rigid CNC so it’ll tend to bounce on and off of the material when doing a full side wall cut like that…

Maybe try skipping the pre-cut and go right into the full depth slot cutting (this puts different forces on the CNC than a side wall finishing pass) and just reduce your feed rate to accomplish the carve…

Thank you Seth. I have not worked with the offset tool before. I will give that a shot.

The fray seems to be on all four sides. I am not sure what you mean when you use the word “tram”. What are you referring to?

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I don’t think the machine is rigid enough to to a straight wall finishing pass but if you want to try it again (you could use an offcut and do some side wall tests…) and try a slightly larger remaining stock of 0.02-0.03" instead of the 0.01 from before…

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Tram or tramming is the process of adjusting the spindle perfectly perpendicular to a surfaced wasteboard.

This video is pretty good… this video shows the process with an X-Carve & Tim’s custom tool…

this video shows the theory much clearer, but it’s not an x-carve so the actual tramming process itself is of course different. I suggest watching both videos BEFORE doing the process.

Thank you Seth

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Also, measure your bits with calipers. Most bit manufacturers will have a tolerance that is allowed. For instance, my 0.25" upcut bit is actually 0.245". Use the actual measured dimension when inputting the bit size into Easel. This will ensure you have the most accurate cut as long as everything else is in line.

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Brandon Parker

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Thank you Brandon. I do that with all my bits.

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@DouglasPauls, I’ve found compression bits, especially in 5/8" or thicker material makes a nice clean cut on top and bottom. Here’s are two I’ve found that work well:
1/4" - https://amzn.to/2WgVPHi
1/8" (w/ 1/4" shank) - https://amzn.to/3gqWwob

Thank you Matt. When you use these do you plunge to the full depth and do an outline in a single pass or multiple passes? What I am trying to get is a smooth sidewall in basswood. But, you have given me an excuse to buy two new router bits. Many thanks.

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Yes to both… you can go full depth as long as you slow the feed enough that the steppers don’t loose steps. OR you can do multiple steps BUT the bottom portion is still and upcut so if you do multiple steps you might (will probably) still get that fray line part way down…

You may have better luck with a down cutting bit. Up cutting bits tend to pull the work piece up, which can cause slight movement. Down cut will push it towards the table, less likely to move.