How do you reduce shanks on router cutters

[Alistair Hosie]

I bought some really good router cutters at an auction thought they would go good in my router table although I laid out about a hundred bucks for all of them they would probably cost that each and more I got about seven or eight of them.Problem is half are half inch 12.5 mm and fit the router collet fine the others actually about five of them are just about a millimeter to wide 14mm approx must have been for a c.n.c miller I've been told.They are too good throw away I made enquiries about having the shafts professionally reduced no body wants to know as the router bit heads have profiles which cannot be re-entered in the lathe chuck without damage or being able to hold true and safe.
I suddenly thought a few days ago that if I was to cover the heads with tissue paper then moulded car body filler paste around them then re-entered them into shank end in to the chuck and trued it up so that it could be reversed then the bit with the car body filler (now trued)could be held in the chuck with the shank sticking out and I could remove the millimeter or so as required any ideas or suggestions as to how this could be done better or would in your opinion would it work I figure with the tissue papes acting as a light barrier I could burn the body filler a bit at a time and prise it off Alistair

[Paul Gauthier]

Your idea may work however i would not use the body filler, use a two part epoxy but coat the tool with a release agent first. If you have no release agent trot on down to you local food store and aquire a can of PAM cooking oil. May be know as something else over there but will probably be the same thing. Makes an excellent release agent. I use it when bedding rifle actions. Don't be stingy with the epoxy (Yea we know about you Scots) and you might want to use a metal rod stuck into the epoxy at 90* to the shank to use as a drive dog. Unless you can fit it into a collet.


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Paul G.

[Peter S]

Alistair,
Sorry to be so unimaginative, but why not try to buy the correct size collet? (maybe it is 9/16" which is 14.29mm).

[SGW]

Another option might be to use one of the low melting point alloys as a fixturing material. There are a couple that melt below the boiling point of water, so there would be no danger of annealing the cutters with something like that, and it would be easy to get off. And the stuff is reusable!

[Alistair Hosie]

Peter s my router wont accept collets above 12.5 mm or if so don't know of router collets that would fit a dewalt of that size as they are pretty well standard. Also would be prohibitively expensive and end up being not worth while router collets for my machine are around fifty U.S dollers here in G.B .
I thought the tissue idea would create more space for the release of the body filler i.e be enough to hold but not enough to be irremovable oil would be fine ordinarily but i feel might be so fine the filler material would possible get into all the little undercut areas and would make life more difficult at the end of the day.I could be wrong Alistair

[JCHannum]

Alistair, try it, it sounds like it has some merit.
I would recommend using a toolpost grinder. If you don't have one, a simple one can be rigged up using a small high speed hand grinder and clamping it to tool post. This would be adequate for small amount you need to remove.
That way the cutting forces would be low, and you will probably need to grind as cutters are most likely hard or HSS.

[C. Tate]

Does the bit have two centers in it. If so you can place between centers on the lathe and turn/grind the shank. Are these carbide tipped? If so you can probably hold shank and center drill if they do not have centers already. The router bits I have seen are forged with a carbide face brazed on and are probably not so hard they cannot be drilled. You may have to rig a small drive dog out of hard wood or aluminum to work between centers.

[This message has been edited by C. Tate (edited 05-21-2002).]

[Alistair Hosie]

Good points lads.
My main concern is obviously the high speed these devils revolve at. If by any degree out of true I'm sure the vibration would be a real danger both to me and the eqipment i.e router There is I feel a strong possibility that they could work looseand even fly out of the collet holder owing to the centrifugal forces, I can control the router speed to a point and obviously the big cutters like these are not supposed to be run at highest speed anyway.There may be some merit C Tate in setting up between centres but I feel that is not on the cards will have to look to see if this is possible. I am not confident enough about grinding the shanks as I don't know exactly how it's done but i've heard of it and somehow I think this might be the best way just not experienced enough to try but thought about applying a file which could traverse the shaft till spot on.You guys will probably laugh at that idea but it just entered my head .

[JCHannum]

A file is not a good idea, as the shank will neither be round nor true. Either use a cutter or grinder. Read up on it, and add to your skills inventory.

[C. Tate]

Alistair,

These bits are not anywhere close to being balanced from the factory. The adjustment you will make to the shank will have almost no bearing on the performance in the machine because you are removing material parallel to the axis of rotation. If you were to remove some steel from the flutes you might then get some vibration. If you can file the shank then you can turn it just as easy.

Just thought of another solution. Suspend the tool between centers on your wood lathe and use a piece of very coarse emery cloth to polish the shank down to the proper size.

[John Stevenson]

Alistair,
Are they long enough to hold just the first bit of the shank at the tool end and turn / grind the rest down stepped to fit the 1/2" collet?, which incidently is 12.7 not 12.5

Try the shank first with a file to determine just how hard they are. If they are solid carbide then you are in trouble without professional help. It they are brazed inserted cutters the chances are you can turn these.
If you can turn then hold them fully in the chuck first and put a small centre in to support for the turning operation. Wrap a bit of tape around the cutting edges to protect the edges and also your lily whites.
With a centre suport you only need to lightly grip on the last 1/8" to allow you to turn the rest down.
Let us all know how you get on.

John S.

[KVollert]

Alistair;

Typically most routers here in the states come with just 2 sizes of collets 1/4 and 1/2 inch as the standard sizes. I don’t see any reason that you could not buy a extra 1/2 inch collet and open it up an extra millimeter using a tool post grinder. I think this would be much easier than trying to grip a router bit and grind the shank with any degree of precision.

Thanks Keith

[Alistair Hosie]

kvollert you are an absolute genius go immediately to the top of the class sounds so easy Im surprised I didn't think of it.This really sounds as though it may work so long as the collet and possibly retaining nut can be slightly enlarged ,I think it will work only problem is collets are quite expensive but the retaining nut should be able to be enlarged and still work for both sizes of collets.Remember prices here for collets etc in fact everything is much more than U.S or Canada.I think a collet for my router is around آ£ 30.00+ approx $45.00+ but still may be the best option.thanks everyone so far response has been very helpful Alistair.

[Peter Sanders]

Hi Alistair

That was my first thought, providing there is enough material to enable a millimetre to be ground away, and you only have to machine one item.

From my experience, the nut that holds the collet should not require any modification as you are only changing the inside diameter of the collett, and the nut (on my router at least) surrounds the top of the collet itself.

Why not turn your own collett, you have a precise example to guide you.

Although router bits may not be balanced per se, they are ground on centres, so they are more or less dynamically balanced due to this process. A small variation in centreline would cause a tiny but noticeable vibration through the router. This vibration may result in a less than perfect finish on the wood.

Also if you attempt to reduce this diameter on your wood lathe using emery etc you may impair the grip of the collet on the bit.

If you ultimately have to resort to your original body filler approach, perhaps you could consider the following...
1. plunge the bit into a piece of hard timber - to create a blind hole shaped to the profile of the cutter.

2. Set the bit (square) in the plunged hole.
3. Fill the hole space around the cutter with car body filler.
4. When hard set the router bit true in the (4 jaw) chuck and (gently) turn the wood surrounding the cutter edges.
5. Mount this truely turned timber in the lathe and grind the shank of the router bit.

You should find that the "blunt" end of the cutter has a centre hole (from the original machining / grinding process) in it. You can use this as an aid to supporting the bit during your machining.

I have thought of some other ideas if none of the suggetions so far are not feasible.

Regards

Peter

<font face="Verdana, Arial" size="2">Originally posted by Alistair Hosie:
kvollert you are an absolute genius go immediately to the top of the class sounds so easy Im surprised I didn't think of it.This really sounds as though it may work so long as the collet and possibly retaining nut can be slightly enlarged ,I think it will work only problem is collets are quite expensive but the retaining nut should be able to be enlarged and still work for both sizes of collets.Remember prices here for collets etc in fact everything is much more than U.S or Canada.I think a collet for my router is around آ£ 30.00+ approx $45.00+ but still may be the best option.thanks everyone so far response has been very helpful Alistair.</font>

[C. Tate]

Grinding or turning between centers aides in concentricity but correction in two planes is necessary to acheive true balance. I would say that most router bits are form relieved and are ground while being held in a collet by the shank the ones that are ground between centers are the ones that use a bearing as a guide. I still say that the amount of imbalance you may get will be negligable. How would polishing the shank to size with a piece of emory hinder the grip?

The polishing method is not the ideal solution I know, but it will work.