Forstner Bit produces Tapered Face

[Mark Beattie]

Hi all. I've been lurking around these forums for a long time and have decided to register and post a few questions. I've been experimenting with different tooling for a year or so and have a question about Forstner Bits. I have bought three different types of Forstner's ( Lee Valley, Canadian Tire and KMS Tools ) and all of them seem to produce a tapered face ( high in the center, tapering out towards the edge ). This is problematic because I cannot properly form the stem / shank face junction. Is it just my eyes or are there variations to Forstner Bits?

Also, I've read a lot of debate or flat bottomed mortises and, until now, I've been drilling my mortises with a standard 5/16". I switched to these because all the brad point bits I've used produce an un-even bottom due to the outer spurs digging in deeper at the perimeter of the hole. Any thoughts on this dilemma?

Thanks in advance. I've really enjoyed perusing these forums.

Mark

[DMI]

Not quite sure how the quality/price compares but the bits all look pretty cheap, I pay £30/$50ca per bit.

You get what you pay for.

David.

[KurtHuhn]

Look for "precision ground" bits from Freud. Those should get you a perfectly flat face without breaking the bank.

[Sasquatch]

Yeah the Freuds from Home Depot are pretty flat. If you buy a cabinet hinge mortising bit, a 35mm one for pocket hinges, it'll be dead flat too, but that a bit large for our purposes.

[taharris]

Forstner bits work well on the stemmel, but I still have trouble getting the sholder on the stem perfectly parallel with the stemmel and I end up with a paper thin gap.

Does anyone have any good tips to help me accomplish this on a wood lathe?

Right now I get it as close as I can with a chisel and then usually end up drilling a hole in a piece of flat wood, surrounding the hole with sand paper, and putting the stem in the hole and turning to improve the flatness.

This gets me very close, but I am planning to make my next pipe with an oval shank, and I need to get the fit perfect.

Any suggestions you can give me would be appreciated.

If the advice is good, I might even promise not to post any more bad haikus

Thanks

[adryazad]

U guys can get these bits from places like Ace Hardware and Home Depot! I'm moving to the US..... hehe.. I get mine through a catalog. But now am looking to buy from from the US because the smallest i can get is 3/8"

[Joe Hinkle Pipes]

i have been using a 1 1/2" freud bit with the point filed off, and it doesnt give me great results on a wood lathe either. Usually the face is square, but it doesnt give a great finish. also if i dont start the process with a different bit, its hard to get the tailstock centered due to the play that a wood lathe has. So i start with a taper bit, chuck it, crank it to the rod stock, center it, back it up, remove and replace with the freud, and crank it in. good fit, but bad finish. I have tried a 6" PSA sanding disk in the tailstock, but at the finer grits it just wears the center of the sandpaper out. I have sold tools for 10 years, and cant think of anything else that may work in the tailstock to give a smooth finish. maybe i shouldnt have filed the point off the forstner bit?

[RadDavis]

maybe i shouldnt have filed the point off the forstner bit?

Probably not. The point and outside edges act as an anchor for the bit while it's cutting with the blades, and keeps the chatter down.

You're gonna drill a mortise anyway, so you might as well have a little pointy pilot hole already there.

Rad

[KurtHuhn]

Yeah, filing the point off was a mistake. It's the only thing keeping it in place.

Try using a fresh Forstner bit first, then drilling the mortis, using the dimple left behind by the Forstner bit as a guide for lining up the mortis bit.

And if your lathe really has that much play, I suggest tracking down the source and fixing it. It might be as simple as shimming the tailstock.

[taharris]

So i start with a taper bit, chuck it, crank it to the rod stock, center it, back it up, remove and replace with the freud, and crank it in. good fit, but bad finish.

I'm confused. Are you using a derlin tenon?

The problem I am having is with the sholder at to bottom of the tenon. I am not using derlin.

Also, I agree with Kurt, you should not have any play in the tailstock if you have a decent wood lathe.

Todd

[Mark Beattie]

Thanks everybody for the information. I'll be checking out Home Dept for a Freud Forstner. Would anybody like to elaborate on te second question I posted here rebating the Brad Point bit (First post at the top)?

Mark

[JHowell]

You don't want a brad point drill for mortises, as you've discovered. Just use a standard twist drill.

As for the Forstner bit, there are two ways it will cut a shallow cone like you describe. First, the bit can be ground that way, or else your tailstock alignment can be out. If you're using a wood lathe, often there's a bit of play in the fit between the tailstock and the bed, and it's important that you get the bit aimed precisely at center before you lock it down. When I used a wood lathe, I always touched the spinning work with a pencil in the center to give myself a bullseye for the bit. Of course, you need the point on the Forstner bit to hit that bullseye. If you're using a metal lathe, forget the Forstner, just face the mortise face off flat.

[Sasquatch]

Mark, don't take this the wrong way, because I'm the king of over-thinking pipes, but you're over thinking this.

Of what advantage is a completely flat bottomed mortise as opposed to a slightly concave one (from say a regular twist drill) or one that has slight (and we are talking what, 1mm?) indentations at the edge?

A brad point would be advantageous in one scenario - they have a little "leader" in the middle and when you go to drill the airway, there will be a little hole dead center in the mortise to get you going.

The mortise should whenever possible be basically filled by tenon - therefore, whatever your mortise shape is.... the tenon should mimic it more or less.

[Joe Hinkle Pipes]

Todd,
Yes, I am using delrin. I have ordered some turning chisels to make an attempt at true tenons. The play isnt extreme, its just noticable. I dont know why wood lathes have it. I have a temporary shim for now just to take up some of the slack. I will probably end up ordering some brass shimming material to try to make a precise fix.

[JHowell]

Todd,
Yes, I am using delrin. I have ordered some turning chisels to make an attempt at true tenons. The play isnt extreme, its just noticable. I dont know why wood lathes have it. I have a temporary shim for now just to take up some of the slack. I will probably end up ordering some brass shimming material to try to make a precise fix.

It's not necessary to shim the tail stock on a wood lathe, and introduces the possibility that you'll fix it in the wrong position. There is no particular requirement that wood lathe beds are flat, or mounted level. A metal lathe is properly set up with a very precise machinist's level that establishes the bed is level and free of twist. The ways are much heavier and more rigid than a wood lathe's bed, and made to present a certain degree of accuracy to the saddle, which carries the cross slide and compound. Since a wood lathe has no carriage, only a tool rest, and since any precision it has depends on the operator's freehand manipulation of tools, only moderate care is taken to make a consistent surface for the attachment of the tail stock. Add to this the possibility that the head stock is not perfectly aligned to the bed, and a bit of play in the tail stock becomes a necessity. What is center in one part of the bed may not be correct a few inches away. Much better simply to "aim" the tail stock for each hole before clamping it down.

[Mark Beattie]

Freud Forstner works great. Perfectly smooth shank face. Thanks Kurt for the suggestion. A note to fellow Canadians: Home Depot and Lowes carries this brand of Forstner bits but only Lowes has them in stock at the store. You have to order them online at Home Deptot.

Thanks to everyone for helping me out.

Mark

[adryazad]

Was surfing woodcraft website and I came across some 'woodriver' forstners, plenty cheap and on the item description says that it produces flat faces.

I believe this is the same bits that I can get from my local supplier. White quality isn't that great, it does it's job, only sad thing is the smallest i can get them here in Malaysia is 10 mm

[Charl]

Same here in SA. Smallest you get is 10mm.