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View Full Version : Help Me Size A Cutter, Of Some Sort???



cds
05-13-2004, 07:04 PM
Hello All,
I am trying to find the best cutter to do this job. I have a cylindrical piece of hardened steel that I need to fit into a .110 deep blind hole.This cylindrical piece is measuring in at .298 wide, and I need to have enough clearance for piece to move easily up and down in the hole but not too much as to allow it to move sideways. It is a button-locking mechanism for a knife and if it moves in the hole sideways it will cause the blade it is locking, to have undesirable play. I cannot find a cutter that is sized to cut this hole. And I do not have the means to re-turn this piece. I see some reamers that are made in special decimal sizes but am not sure if reamers are meant for blind holes. I thought also about a 19/64 center-cutting end-mill, but again am not sure of the tolerance of the mill as it comes in at .296875. This is a prototype knife I am making and am trying to keep the cost of the tooling down. I was hoping maybe someone could see what I was trying to do and spot out the right tool before I go spending alot on the wrong cutters. Any help is greatly appreciated.
Chris S.

gglines
05-13-2004, 07:29 PM
Chris:

I'd grind a small boring tool and bore the hole to the fit you want after drilling an initial hole. You could do this on the mill with a boring head or on the lathe.

George

darryl
05-13-2004, 08:21 PM
Do you have any spare pieces of that hardened steel? Maybe you could grind some teeth in one end of a piece of hardened steel, there's your bottoming cutter. You'll need a hole first that is undersize by something less than the thickness of that steel cylinder. Do a test, and if the hole it makes is too large, you won't have much material to grind away to reduce the hole size. Use cutting fluid to maximize the life of the makeshift tool.

cds
05-13-2004, 08:28 PM
Thanks guys! Are there any reamers that are made for blind holes? Thanks!
Chris S.

Paul Alciatore
05-14-2004, 11:44 AM
I've never seen a reamer without a small bevel at the tip. That would leave a chamfer at the bottom of the hole. I believe this is done to help guide the reamer into the hole in a centered manner.

You could call some of the manufacturers and ask.

Or, you could just buy one and grind the end off. If you make it completely square, I would buy two and use the unaltered one first to start the hole, then the reground one to finish.

What I would do is find the reamer with the smallest possible bevel (or grind one down a bit to leave just a small bevel) and chamfer the edge of the button to match. This will help the button to "find" the hole when it is being engaged. It will make the knife a lot easier to use and will help to loosen the tolerances on the location of the button and hole. A lock with a tight fitting button like you describe will require very tight tolerances to allow it to work at all.

Actually, I would also try to use a slightly tapered design on the button and hole so it can seat tight with no play. One degree or even less taper may help a lot. But this may require a specially sharpened reamer and may be expensive. And you may need a feature to unlock it.

Paul A.

coles-webb
05-16-2004, 09:32 PM
KBC Tools sell machine reamers in sizes from 0.030 to 0.9995 in increments of less than 0.001. ( page 83)They will have a chamfer on the end (that's what does the cutting) but if you use one to ream to size and then grind the end flat (remove chamfer) on a second reamer, it would remove the little bit left at the bottem of the hole. You can grind it by hand it you are carful, use a toolpost grinder in the lathe or a home made toolpost grinder such as the one I posted at the other link.

Mike

http://www.kbctools.com/can/main.cfm

http://bbs.homeshopmachinist.net//Forum1/HTML/006553.html



[This message has been edited by coles-webb (edited 05-16-2004).]

drof34
05-16-2004, 10:05 PM
make the hole first with a 9/32 end mill.Then flatten the end of an N size drill. go slow in and right back out. Should give you .004 clearance,if that's not too sloppy.
Jim W.

John Stevenson
05-16-2004, 10:07 PM
Chris,
First off 'drill' the hole undersize but to depth with a centre cutting slot drill or end mill 9/32" diameter.
This will leave you about 15 thou to remove.

Then take a piece of 5/16" drill rod or silver steel about 2" long and turn 1/2" of each end down to your finished size.
On one end ONLY put a slight chamfer.

Then mill away half the diameter for the 1/2" length so you finish up with a 'D' shape looking at it from the end. This is called a D bit. Do both ends.

Then harden this by heating up to cherry red and quenching, polish both flats up with emery cloth and reheat the middle until the polished ends just reach a light straw colour and re quench.
This is now hardened and tempered for cutting steel.
Using a fine sharpening stone clean the flats up so you get a sharp cutting edge with what's left of the OD

Using plenty of cutting oil and a slow speed open your pre drilled hole up using the end with the slight chamfer. Retract, clean and repeat using the other end to get a flat bottom.
Practise on a piece of scrap first.

John S.