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Re: beveled edge table top

PostPosted: Thu Mar 14, 2019 11:35 pm
by Pete Cyr

Re: beveled edge table top

PostPosted: Sun Mar 17, 2019 2:01 am
by duster
Update: For a test, I drew this as a 14" diameter circle and applied a 45 degree edge vector to cut 1.75" deep into a 2" thick piece of foam. Rough cut was with a 1/2" end mill, finish cut with a 3/8 ball nose. It cut very well with good smoothness on the bevel.

The only issue was it only cut about 1.625" deep, instead of the 1.75" I specified. Z zero was set at material surface, so I'm not sure why it didn't cut as deep as I wanted... This would be an issue when I go to cut my 40 x 60 x 2.25 oval, because I'll need to cut all the way through.

Any suggestions on what I should have done?

Re: beveled edge table top

PostPosted: Sun Mar 17, 2019 4:46 am
by 4DThinker
When using a ball nose bit and the moulding toolpath, the toolpath generator keeps the ball end tangent with the 45 degree slope. The bottom of the ball nose stopped at 1.75" but the tangent edge wasn't at the bottom of the bit. I quickly drew up a 1.75" wide/deep 45 degree line and a 3/8" circle to represent the 3/8" ball nose bit. When the circle bottom is aligned with the line bottom the tangent point is 1.6951 from the top according to Aspire. Using a smaller ballnose bit will get you closer to the bottom, but the only way to make sure the tangent edge gets to the bottom is to extend the 45 degree line down. For a 3/8" bit the line should go down (vertically) another 1.75" - 1.6951" or .0549". This will cut into your spoilboard unless you shim up your work 1/16" or so.

4D

Re: beveled edge table top

PostPosted: Sun Mar 17, 2019 5:37 am
by duster
Ok, that makes sense. I'll have a mdf spoilboard under my walnut slab, so if I go 3/16 deeper I should be able to cut all the way through. Thanks! (I'll test this in foam before I try cutting $1200 worth of walnut...)

Re: beveled edge table top

PostPosted: Wed Mar 20, 2019 3:08 am
by duster
So I'm about to try another test to see if I can cut my beveled edge all the way through my 2" thick piece of foam
so I can get my 45 degree edge all the way to the bottom.

To enable my 3/8 ball nose bit to cut through my 2" foam, I set up my job size as being 2.25 thick. I'm thinking this
will enable my ball nose to cut through into the spoilboard about .2", which should give me a clean cut through.

However, when I ran the preview I noticed that the 1/2" end mill I'm using for clearance doesn't cut beyond the
perimeter, and the 3/8 ball nose bit is actually making the last cuts in the full depth of the material. That will be
a problem because my ball nose bit only has a cutting edge of 1.5"

I did a quick search and found that ball nose bits with a cutting edge length of 2.5" are 3/4" diameter, and run about $300...

So now I'm wondering if there's a way to make my 1/2" end mill do the clearance cut a little wider so my 3/8
ball nose can finish the profile with just the tip... Any suggestions?

Re: beveled edge table top

PostPosted: Wed Mar 20, 2019 3:58 am
by gkas
I Added a first Step - Widen Cut. I used an allowance offset of -0.25 and cut another outside cut with a -0.5" bit. Adding the extra material thickness make it tough to see the results of the cuts. I reset it to 2". Trust the preview. Now your 0.5" bit will widen the cut.

Widen Cut.jpg


Elipse test 1 15w x 10h x 2 thick 3D preview (1).zip
Zipped the crv file to compress
(714.92 KiB) Downloaded 40 times

Re: beveled edge table top

PostPosted: Wed Mar 20, 2019 4:26 am
by duster
Ok, I think I get it... except for how do you get the widen cut? I don't see that in the moulding toolpath commands.

Re: beveled edge table top

PostPosted: Wed Mar 20, 2019 11:16 am
by gkas
Look at the crv file I reposted. I added a 2D Profile Toolpath to your vector to the outer edge. I said to mill that before the moulding toolpath is run. This will carve away room for the ball nose to plunge all the way through the material.

Re: beveled edge table top

PostPosted: Wed Mar 20, 2019 4:44 pm
by adze_cnc
gkas wrote:I used an allowance offset of -0.25 and cut another outside cut with a -0.5" bit.


I'd have just run the cut "on the line" instead of "outside" with an offset.

Re: beveled edge table top

PostPosted: Wed Mar 20, 2019 5:08 pm
by adze_cnc
How about the following solution using the previously posted ellipse test. Profile cuts only. If this were a real cut I'd optimize things a bit. I'd overlap the cuts. I'd tweak the depth of cut for each pass. I'd determine the exact angle of my "90 degree", etc.

This method was done on the bottom chamfer for this vacuum-form mould.

in-progress.jpg
Long chamfer just before last pass


Steven

Re: beveled edge table top

PostPosted: Thu Mar 21, 2019 3:15 am
by duster
Update 2: I added a 2D profile cut on the outer ellipse line as per gkas's and adze's suggestions to make clearance for my 3/8 ball nose to cut the bevel. This time it cut the bevel great, and I was able to cut all the way through the 2" foam. I think I'm ready to try it on my walnut panel... Thanks again for all your help!