Cutting 1/2 in BB

[dubliner]

I just found out you cant use tabs with a compression bit, as I get a poor edge at the site of the tab, also what's the best way to drill hole without a drill and not blow out the back of the hole. Otherwise great quality cut both faces with a Centurion 3/8th compression bit. TIA I have to cut two more out so I'll wait for replies tx guys Neville

[curtiss]

I ran across the "spiral cut option" on the Vectric toolpaths that I like pretty well. Say you have a piece .8 inches thick. Use say a 1/4 end mill with a pass depth set at .2 inches.

The tool will make four laps around the work getting deeper each time. Each lap will cut down .2 inches. The final 5th /lap will run at .8 to drop out the piece.

I slide in a few 1/4 pieces of wood on the final lap so the piece does not move. You might slow down on the final lap. No tabs needed.

[zeykr]

The tabs should work fine with compression as long as the tab is thin enough that the upspiral part of the compression stays below the surface of the material when raising up to cut the tab. Maybe a .125 high tab when using a m/c bit with .25 up spiral.

[dubliner]

Yes Ken, thats what I did, .125 high x .2 long, it leaves two marks that look like Chatter, yet the rest of the edge & rounded corners are smooth as can be. I'll check for pinions and the usual suspects, but I may move to the "onion skin" method. Haven't used it yet successfully though. Curtis a question, 4 laps at .2 is .8, so what does the last pass do? Is it a built in "Onion Skin" routine?

[knight_toolworks]

I broke my last downcut bit and had to get a 1/8" straight bit 2f. I was pretty impressed with the cut the bottom was pretty much fuzz free and the top was fine too.

[curtiss]

As before, the spiral cut starts at 0 depth and gently gets deeper all the time.

In the setup stated, the first lap will cut a perimeter slope that ends at .2 on the first lap. It continues to spiral down with each lap till it reaches .8 and makes the final lap at .8

The z has no sudden drops with this setup which can sometimes chip something out as it drops.

You get to it off the ramping tab in Vectric. Works pretty smooth, try an air cut on a simple rectangle and watch the z gently drop.

[ken_rychlik]

Neville

Run an onion skin cut in climb and a finish pass in conventional and you will like the results. Your bit should be fine.

As for the hole drilling, the best thing you can do to help that is resurface the spoil board. All drill throughs are going to have a little edge on the bottom unless you do them with a smaller bit and make a spiral cut with the bot.

Kenneth

[Gary Campbell]

Nev...

Tabs work well with compression bits. 3D tabs work better. In material 1/2" or less try a mortise comression. It has a shorter upcut. Fred at Centurion has good ones.

IF you dont have a correct sized drill, use a spiral toolpath. Works great for the circular pattern, I dont feel they are aggressive enough for rectangular geometry. Also you need to plunge .25 to .375 for the MC or Comp bit to not tear up the surface.

If your hold down is good enough, toolpath like this for outlines:(assumes 1/2" material, adjust for yours)
3/8 comp or MC bit at 4ips set stepdown to 1" RPM 11,000
1st pass climb start at 0, cut depth .47
2nd pass conventional cut depth .510

[dubliner]

Curtis - sorry, now I get you. I'll take a look at it.
Kenneth i need to refine my "Onion skinning" process. I will try that as a tool to have in the arsenal.
Gary - I'm using a Centurion 3/8th, I was just in the shop and I moved the leftover sheet from the cutouts and I noticed the scrap edge was perfect, so I need to switch the cut direction and remember it, the tool did cut beautifully though. PS Sorry you wont be in Durham. Thank you all for your guidance.