Bit for flat-bottomed holes?

[Brian Leavitt]

Last year I did a sample for a customer. This is a government fella who needs 100 boomerangs engraved and also to have a coin flush-mounted with the face. The sample I did before was easy. I simply engraved it, made a hole part of the way through with a Forstner bit, and glued the coin in. Now, that was nearly a year ago. Today he came back in with almost the same type of boomerang, but this one, along with the other 99 I have to do, are much thinner than the original boomerang.

So now I have a dilemma. I need to be able to recess this coin into the boomerang without any hole coming through the back side and a regular Forstner bit will no longer work due to the "spike" in the middle. I've tried to find a Forstner with a totally flat face, but have been unsuccessful.

I need to make a hole 1.75" in diameter and roughly an eighth of an inch deep into this thing. Can anyone suggest a bit I could use which has a completely flat face? My last resort would be attempting to modify the Forstner bit I have, but I'd like to avoid this, if possible.

Thank you.

[Adam Herman]

can you make a jig to do this with a router? You may try an end mill as well, though i think edge tearout could be a problem.

[Alan Caro]

Brian Leavitt,

It's not fine woodworking, but as the depth is so shallow, how about cylindrical grinding bits in a drill press?




Alan Caro368562

[Chuck Nickerson]

Last time I checked ConValCo made forstner bits with a very short point. Of course they cost more.
You could also buy a spare bit and use a grinder or Dremel to grind away the point.

[Jim Morgan]

$16 for a Freud 1-3/4" Forstner bit at Amazon, just file down the center point. Or get a Grizzly end mill for ~$70.

[Charles Wiggins]

can you make a jig to do this with a router?

This would be my solution. I'd use a straight bit and a collar, then size a circle through a piece of plywood to make a single use router table. Then rig up a clamp system to hold the pieces underneath.

[peter Joseph]

Removing the center point of a forstner bit will have it wandering all over the place unless the piece is clamped extremely well and the press has zero runout. +1 for the router jig.

[Prashun Patel]

I also would use a router and a template. I would use a 1/4" spiral bit with a bushing to minimize the chance of burning.

[Jim Morgan]

Removing the center point of a forstner bit will have it wandering all over the place unless the piece is clamped extremely well and the press has zero runout. +1 for the router jig.

Work needs to be clamped in any case. Make a 2-part jig. Bottom had stops to restrain x-y movement of the workpiece and is longer than the top so it can be clamped to workbench or drill press table. Top can be hinged to bottom, has a cut-out for bit (just drill a hole before filing off the tip) or router template. If using a forstner bit, cut-out eliminates wandering because you are indexing from the perimeter of the bit rather than its center.

[Edwin Santos]

Work needs to be clamped in any case. Make a 2-part jig. Bottom had stops to restrain x-y movement of the workpiece and is longer than the top so it can be clamped to workbench or drill press table. Top can be hinged to bottom, has a cut-out for bit (just drill a hole before filing off the tip) or router template. If using a forstner bit, cut-out eliminates wandering because you are indexing from the perimeter of the bit rather than its center.

What Jim describes will indeed work. The top part with the cut out hole for the bit to travel through is what will keep it from wandering even though the point is ground off. This is also a good method when you need to accurately enlarge an existing hole or when you need to drill a semi-circle or partial diameter hole.

[Mike Cutler]

WL Fuller, Series 060, Forstner bit. Page 74 in their current catalog.
No centering spur. It is guided by the leading edge at the outer circumference. It leaves a perfectly flat bottom. It comes in all sizes, but the shank size changes as the bits get larger.

WL Fuller only makes, and sells, cutting tools, bits and mills, for metal and woodworking. It is all they do. Located in Rhode Island.
If you can describe it, they can make it.

[Brian Leavitt]

Thank you, guys, for the information and ideas. I think I'll go with the WL Fuller bit, as long as my customer will approve the additional cost. It's exactly what I was looking for. Something I neglected to mention in my original post is these are actually polypropylene boomerangs, so I need to use a low-speed method of cutting them. These government folks get some strange ideas for awards...

[Rick McQuay]

I used to have some Forstners without a point and they worked fine as long as the work was clamped tightly but I sold them because they clogged very quickly. It was a weird design, very shallow, very clean cutting but poor at chip ejection. In retrospect I suppose clogging doesn't matter too much because you'd most likely use them with shallow holes. I bought them at auction and don't remember a brand or anything. They may have originally had points and someone ground them off. Don't know. But they are gone now.

[Wayne Lomman]

Router jig. Definitely the way to go. Cheers

[johnny means]

Actually, forstener bits are guided by the outer edges. One of their best uses is angled hole where the spike won't even contact the work piece until well into the cut.

[glenn bradley]

Removing the center point of a forstner bit will have it wandering all over the place unless the piece is clamped extremely well and the press has zero runout. +1 for the router jig.

I have not found this to be the case using a Freud bit. If the material is held to the drill press table well, the rim does fine in maintaining center. The bit you start with does have to be reasonable quality so that the rim is sharp and well formed. The Fuller bit Mike C describes is a commercial version. I'm assuming your engraver is not able to do the hole.

How much dimple can you stand? Even a 1/16" spur will help in guiding the path. You could grind a "regular" Forstner spur down to that. Since you are doing so many I would think a jig for the drill press would be the efficient way to go. Your DP would need to be capable of consistent depth holes within the tolerance you require, of course.

To the chip clogging issue, bit speed and chip ejection go hand in hand. If you experience clogging, experiment with your bit speed to find the sweet spot.

[Mike Cutler]

Glenn

It was only sheer luck that I remembered they had that bit.
I was at a Woodwerks show many years ago in Springfield Mass, where incidentally I met our Dave Anderson of NH, and Bill Hylton. I bought some large brad point bits to repair some boat railing, from the WL Fuller display, and they had a display showing silvers dollars epoxied into wood, and the bit used to do it.
Why I remembered that I don't know??

[Ted Reischl]

Weird stuff like this is what leads to the sales of CNC machines.

[Jay Nossen]

Actually, forstener bits are guided by the outer edges. One of their best uses is angled hole where the spike won't even contact the work piece until well into the cut.
Johnny,
Until you mentioned it, I was in the "center spike contact is needed" camp. Of course, now I remember that I've used them for many a baluster hole in a stair railings, proving you quite correct.

[Brian Leavitt]

Definitely glad, and appreciative, that you remembered that Fuller bit, Mike. I couldn't find anything like that in my searches.

Glenn, No, the laser will not do a hole like that into Polypropylene. With this type of plastic, it simply melts and flows right back into the lasered area. I don't even like lasering text into this stuff because I think it looks terrible, but my customer likes it so I'm doing it. I am going to use the jig/drill press method here, and I'm passing the cost of the bit right on to my customer.