Tools marks by tabs/bridges

[bd007]

I am using tabs to keep my cutouts from flying all over the place but I can't seem to get rid of the tool marks by the tab. There is one on both sides of the tab from the raising and lowering of the bit. Any ideas or suggestions to prevent these marks? Are these common with tabs? I may have to switch to double sided tape.

Thanks
Dave

[Madclicker]

These are caused by the flex in your machine. When you are cutting, there are tangential forces acting on the bit caused by the cutting action. If these are greater than the flex of your machine the bit moves sideways during the cut. When you stop at the tab everything relaxes and the bit moves back to where the spring in the machine wants it to be.

Only fix I know of is a stiffer machine or slow it down.

[HuFlungDung]

Don't just stop, lift and plunge where the tab meets the part profile. Create a small lead on and off the part profile. Also, this lead on and off should actually be drawn with a small radius, rather than a simple 90 degree square corner. The radius should be a little larger than the tool radius so the the tool can actually move along the radius as it leaves the part profile.

[bd007]

Thanks for the replies. I tried a couple of things and got mix results. I tried the leadin and also changed the cutting direction. I was cutting clockwise and changed it to counter. The marks are completely gone!! By changing the direction I am now seeing a layering effect on the side of the part. You can tell exactly where each cut depth was. When I was cutting the other direction it looked like I cut it at one pass. This was an issue I had on my jrgo and now I see on my new machine. Any suggestions? I am cutting 1/2" mdf, at 35 ipm, 1/8" upspiral, 4 passes.

Thanks
Dave

[Rance]

Dave, You are seeing the result of flex in your machine. Do 4 passes in clockwise direction (roughing), then do a duplicate 4th pass in counter clockwise direction (finish).

[bd007]

Thanks for the cutting tips. I will give it a shot this weekend. Sounds like it should work.

I am also looking into Vcarve since it offers 3D tabs. I think thats what HuFlungDung was saying to do.

Thanks everyone!
Dave