Straight Plunge/Drilling (3/4") diam bit application problem

[c.fehringer]

Hey guys,
I am a long time viewer of cnczone, and finally I need some help on something Im having a lot of time caught up in. Heres the deal.

We are engineering the manufacturing line for a new business, and i have run into a problem that isnt all that typical of an operation to my knowledge.

I need a router bit that is mounted in a porter cable 1_3/4 hp router within a special jig setup. The bit needs to be exactly 3/4 o/d straight plunge by 3/4+ cut height with a 1/2 shank. It also needs to leave a flat cut in the material on the bottom of the plunge. I am using this as a straight plunge directly vertical into the material, ie there is no shear or climbing of the cut. An example of this would be to put the bit into a drill press and plunge a hole into the material (im using it like you would in a drill, to make a 3/4 hole). It CANNOT leave any type of nipple facing outwards at the bottom of the plunge, like most bits would.

I have contacted Amana Tool (which I have spent an arm and a leg on router bits with) and they arent very helpful. After a few tries and suggesttions they recommended their super plunge bit (part number 41438). The problem with this bit is it also leaves a nipple on the material, and doesnt cut worth a **** (the dimensions are correct but the bit just wont cut). I am milling end-grain, quite hard gunstock type plywood. The router has enough power and doesnt bog down so the 1_3/4 hp isnt a problem.

I need something that will make a clean plunge and also doesnt smoke and start my shop on fire. The bits that I have been recommended cannot even bore softwoods without almost starting on fire. I dont care what type of bit it is as long as it cuts a flat bottom, cuts without smoking on the first 1/16th inch of a brand new bit, and can handle some manufacture type usage. Cost is not a big deal as long as its not custom made. It has to fit in a high speed router, ie, no forester bits or anything like that.

Thanks a lot,
cf

[txcncman]

What does not custom made have to do with it?

Get a 2 flute center cutting HSS end mill and have the shank ground to 1/2" diameter.

[louieatienza]

There's almost always a tiny bit of clearance in the center of a straight bit since the center cannot truly cut. You're trying to cut with the most inefficient part of the bit! Amana does make plunge straight bits with a center plunge blade, though I don't have the catalog in front of me.

Personally I'd pocket this with a 1/2" bit, unless you want to do two ops, one to remove the "nib."

End grain is normally tough to drill anyways, and usually at slower speeds than a typical router. Even with a Forstner bit on a drill press, it still would be a slow-go.

[ger21]

I'd do a helical cut with a 1/2" bit as well. Any 3/4" diameter bit plunged repeatedly will generate tremendous heat and dull quickly, which leads to the burning you're seeing.

[txcncman]

I think he was pretty adamant that this has to be done by plunging. Another option is to use 2 tools. Use a 1/2" diameter tool first, then the 3/4" diameter.

[low_48]

The bit you want is called a center cutting straight bit, if you want straight carbides. If you want cheap; MLCS Plunge Cutting Straight Router Bits

Lee Valley has a high speed steel spiral upcut, part number 86J01.42. It might not last long in the plywood, but maybe you could get it coated in Titanium Nitride to make it longer lasting.
Onsrud Spiral Router Bits - Lee Valley Tools

[c.fehringer]

Thanks for your input, I appreciate it. I tried using a 1/2 plunge/pocket followed by a 3/4 inch bit, and we are still having some major problems due to depth of cut on the 1/2 inch. I believe we are going to have to switch the design to something else, or figure out another method, i.e. not a router, to make it happen.

Thanks again