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ryanjg117
01-29-2017, 03:49 PM
I have a new project that calls for more than 200+ holes cut into 25mm thick baltic birch plywood, for each platform. My overall project calls for more than 100 of these decks, so lots of hole cutting!

I created a prototype using a down-cut spiral end mill bit, I believe it was 3/8" in cutting diameter. However, it left burn marks at the bottom of each 1/2" hole. I've since been told that "3D entry" could resolve this issue, but I'm sure if my friend's CAM software supports that. The bottom of all holes must be flat.

One other note: I also need to cut sub-holes inside these 1/2" holes that will be 1/4" in diameter. We do have a dual-spindle, so I can configure these smaller holes to be cut with a smaller bit.

In general, I guess I'm just wondering what the perfect bit would be for this kind of application. And any idea of how much mileage I will get out of each cutter before they need to be tossed or resharpened?

Thanks!

ger21
01-29-2017, 04:40 PM
I would use a solid carbide drill bit for the 1/4" holes, and drill them first.
Then follow with the 3/8" downcut with a helical toolpath.
The 1/4" hole will provide some clearance and greatly extend the life of the tool. Since those are small holes, the feedrate will be fairly low, so try to keep the rpm as low as possible to maximize tool life.
I'd recommend a downcut bit with a harder grade of carbide, like a Vortex XP.
https://www.vortextool.com/index.cfm?fuseaction=category.display&category_id=135&CFID=28563823&CFTOKEN=4bbb4a7f26fbc4aa-39B906D6-D625-A3E1-D5F089BBBA600C0D

ryanjg117
01-29-2017, 05:39 PM
I would use a solid carbide drill bit for the 1/4" holes, and drill them first.
Then follow with the 3/8" downcut with a helical toolpath.
The 1/4" hole will provide some clearance and greatly extend the life of the tool. Since those are small holes, the feedrate will be fairly low, so try to keep the rpm as low as possible to maximize tool life.
I'd recommend a downcut bit with a harder grade of carbide, like a Vortex XP.
https://www.vortextool.com/index.cfm?fuseaction=category.display&category_id=135&CFID=28563823&CFTOKEN=4bbb4a7f26fbc4aa-39B906D6-D625-A3E1-D5F089BBBA600C0D

Thanks for the advice. For the 1/4" holes on the first pass, I suppose I could use a spiral upcut with 1/4" cutting diameter, right? Since surface tearout isn't really an issue as the 3/8" bit will take the next pass, albeit shallower. I'm assuming an up-cut will help with chip evacuation and should eliminate the chance of burning as well?

If I'm still getting burning with the 3/8" downcut boring out those 1/2" holes, what about the idea of using this but only to penetrate the surface, then using a 3/8" upcut spiral for the deep boring?

Just one more random thought: I have a big lot of 5/16" Osrum down-cut spiral end mill bits. My friend got them for about $2 apiece. Not ideal for this app, but if you have an idea on how I can use them, maybe it would save me a few bucks.

The Vortex bits look awesome but at $100 a pop, and given this is a semi-hobby/production project, not sure if the budget will allow for that.

Thanks!

P.S. Better idea: since the CNC machine only has two spindles, what do you think of using (a) 1/4" spiral up-cut bit for the 1/4" holes, the 3/8" downcut for 90% of the hole boring, and then go back to the 1/4" spiral up-cut bit to finish out the bottom of the holes, eliminating any burn areas?

P.P.S. What feed rate would you recommend for each bit, and what depth of cut per pass?

ger21
01-29-2017, 06:00 PM
No, use an actual 1/4" drill bit, solid carbide. Even with an upcut bit, plunging will cause burning.

Feedrate may be limited by the machine. Go as fast as the machine will let you.
But don't plunge, make a helical cut. With the 1/4" hole already there, you shouldn't get any burning. I'd probably cut about 3/16" - 1/4" per pass, maybe more. As much as you can get away with and still get a quality cut.

ryanjg117
01-29-2017, 09:46 PM
No, use an actual 1/4" drill bit, solid carbide. Even with an upcut bit, plunging will cause burning.

Sounds like a plan - except for the 1/4" holes, a flat bottom is necessary. The drill bits would leave a funnel-shaped bottom, correct? Is there such a thing as a flat-bottomed drill bit?

ger21
01-30-2017, 08:10 AM
Yes, but they'll leave a dimple in the center and cut deeper around the edge, because they have a center point and spurs.
https://www.vortextool.com/index.cfm?fuseaction=category.display&category_id=72&CFID=28571714&CFTOKEN=9e25632fbdbf5b3e-5AF59115-E31F-18F8-2BA31484D68FE846

CNCMAN172
01-30-2017, 08:17 AM
Like Ger21 said drill them with 1/4" solid carbide drill, if they need a flat bottom you will use a flat endmill in the next operation that does helical cut that will enlarge the holes. I did this same approach to put in threaded inserts in my CNC table. Works perfect.

Russ

bevins
01-30-2017, 08:21 AM
I would use a .235 drill bit to drill all the holes becasue it will be faster, then switch to a .25 endmill to do a finish pass on the hole, and use the .25 endmill to do the 1/2 inch pocket.
Use some kind of spiral ramp for the 1/2 inch pocket.

Just my thoughts.....

Bob

ryanjg117
02-12-2017, 08:07 PM
I'm going to try the drill bit followed by .25" end mill for the finishing pass. For the first pass, it's not necessary that it be a flat bottom, since that will be addressed on the follow-up pass.

Rather than using a .235" bit, I'm just going to use a .25" bit (since the final holes will be slightly oversized, I'm guessing .275").

Would this be a good bit for the first pass:
1/4" Solid Carbide Jobber Drill Bit 2-Flute 118* PT, 550-2500, U.S.A., G4 | eBay (http://www.ebay.com/itm/1-4-Solid-Carbide-Jobber-Drill-Bit-2-Flute-118-PT-550-2500-U-S-A-G4-/141400459249?hash=item20ec1fc7f1:g:zHMAAOSwxvxW7WAj)

Also, for the drill bit, what would the desired feed rate and RPM be? The CNC machine I'll be using can go up to 400 IPM.

Thanks!

CNCMAN172
02-12-2017, 08:57 PM
If you are drilling wood just use a regular or brad point drill, I tried a solid carbide which works great in aluminum but can burn in wood

Then follow up with an endmill smaller than quarter inch or use quarter with helix cut but watch out on you depth of cut on the helix

louieatienza
05-24-2017, 06:15 PM
Use 3/8" and 3/16" endmills, and helix down.