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Old 05-31-2020, 06:52 PM
cncdood cncdood is offline
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Join Date: Dec 2018
Location: Austin, Texas
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Default No long 1/4" downcuts to be found

I'm hoping to laminate two sheets of 3/4" ply together to make a ~1.5" thick piece of stock that I then hope to profile cut on my Cobra. My goal is to laminate before I cut for a variety of reasons. Finally, my cut has 1/4" radius inside fillets.

So I was hoping to find a 1/4" downcut bit that'll handle this, but I can't find one anywhere and I'm wondering if that's just not a thing. ToolsToday has this upcut version, but I'd like to avoid tearout on top.

Any ideas?
Austin, TX

2013 Cobra 510 w/ ATC
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Old 05-31-2020, 07:09 PM
Gary Campbell's Avatar
Gary Campbell Gary Campbell is offline
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Location: Marquette, MI USA
Posts: 3,042

1/4" radius = 1/2" diameter bit???? Use a compression bit, you will never get a downspiral to cut 1 1/2" deep without a 🔥
Gary Campbell
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Old 06-01-2020, 09:13 AM
de5 de5 is offline
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Join Date: Jan 2011
Location: Honea Path, SC
Posts: 920

Because downcut bits are more expensive than upcuts, I use them sparingly. I cut the profile .15 deep with the downcut and then finish the with the upcut bit. No tearout at the surface and the downcut bits go on for months.
Charlie Hind
Cobra 404 ATC with 12 tool positions & 4th Axis (2012-present)
(2006-2012 - K2 CNC... sold in 2012 to buy the Cobra)
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Old 06-01-2020, 01:32 PM
Jim Becker Jim Becker is offline
Join Date: Jan 2018
Location: SE PA
Posts: 1,648

That's too thick to do the full cut with a down-spiral for the reasons'll hear the fire engines coming and the kerf will be amazingly impacted even if you don't have flames.

Do an initial cut with a down-spiral to insure a clean top edge and then do the remainder of the cut with an up-spiral. If you can, use something larger than .25", too, to avoid well as the cutting length of .25" bits generally doesn't exceed about 1.125" or so. The long, relieved shank .25" bits (like Amana's) can get deep but I find it has a lot of chatter and I can rarely get a clean cut on thicker material for it. I'm using a .375" up-cut for most of this kind of cutting on my Stinger II with an allowance and a final pass at full depth. If the material surface is delicate, I absolutely hit it with a down-cut first for 6-10mm of depth (.25"-.375") and then use the stouter tool to do the hard work.
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