Cutting Dados

[gkas]

Sometimes I screw up even the simple things.

I'm making a simple wall rack from pine. I decided to use the CNC to cut the dados..... cause it's there.

I'm cutting the left and right sides from separate files, because the back is grooved for backing and the shelves are unequally spaced. I want to cut 0.79" dados 0.5" deep. I initially set it up for 0.75" lumber thickness, and 0.75" dados because I hadn't yet bought the lumber. I cut it with a 0.5" bit. It ran OK, except I noticed that the lumber was 0.79" thick. It took a few minutes because the stepover was about 10%, but came out nice. When I noticed that I needed a recut, I changed the drawing width to 0.79" and decided to change the stepover to 60%. I throw on the right side file and cut it. The actual dados are like 0.55 wide!! I kept checking the file and regening the code, but the cuts didn't change. When I measured the software cut preview with the cursor, it looked about 0.75 wide. Recut on the CNC and the width is still way too narrow. I don't have a sample to post because I screwed around with the files too much and they're not accurate.

Does a stepover have to be fully used? Example: A 0.5 bit in 0.75 slot. If stepover exceeds 50% (0.25") will it still cut the slot? This question may sound dumb, but I can't get my head around why the dado is cutting too narrow when AFIK I only changed the stepover to a large percentage.

[ger21]

I just draw a "U" shaped slot or rectangle 0.75 wide, and do a profile cut inside. Just takes two passes.

[mtylerfl]

You might want to post a file sample so we can peek at your layout and bit assignments. Troubleshooting a dado cut shouldn't take too long.

[gkas]

You might want to post a file sample so we can peek at your layout and bit assignments. Troubleshooting a dado cut shouldn't take too long.

It'll be a few days (Jury Duty). I'm not sure which is the problem file after messing around so much. I'm going to create another rack after my jury duty is over. I'll design it from scratch and see if I have the same problem.

thanks all

[Adrian]

From your description the attached file is what you were doing (I've created both types of pocket as you didn't specify what you were using). They all come out as the same width in the preview and I've checked the code as well which is also accurate.

Usually if that is the case it points to a machine issue but that's a big discrepancy to be free play etc in the machine but a 60% stepover would be a lot more force than a 10% cut.

[gkas]

Flatten.crv

(35.5 KiB) Downloaded 79 times

OK, I got a test example set up. And I'm getting more confused. The piece is a 6"x4" block and to be planed slightly. Both examples use a 1.5" bit. The only thing changed is the stepover. The first has a 6% stepover, and the second has a 51% stepover. Why does neither go edge to edge? Also, the total cut is less with the larger stepover. Why?

Flatten.crv

(35.5 KiB) Downloaded 79 times

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While getting this post ready I realized my entire problem. When using a raster cut, you HAVE to make a profile pass, even if it is 0.0. That is the cleanup cut. I thought it was just for cleaning up the pocket edges. I retested everything, and it all works like I thought it should, as long as I include a profile pass. I'm posting this anyway to follow through with my original question.

[joeporter]

"While getting this post ready I realized my entire problem. When using a raster cut, you HAVE to make a profile pass, even if it is 0.0. That is the cleanup cut. I thought it was just for cleaning up the pocket edges. I retested everything, and it all works like I thought it should, as long as I include a profile pass. I'm posting this anyway to follow through with my original question."

The clean up pass is an option in a drop down menu when calculating a Pocket toolpath when using the Raster choice. There are three choices; None, First, and Last. I usually chose the "Last" option. I am not sure what you mean by the "0.0" that is referring to the Raster angle, not an amount to be removed, etc.

Just another thought from looking at your example, your outer vector and any dado type vector can and should extend well beyond you material boundaries to get a clean through cut. You just don't want your vectors to extend beyond your machine limits Hope this is of some help...joe

[gkas]

The 0.0 was referring to the Pocket Allowance.