[timlkallam]

Our shop bid on this job brazing a caride drill on a threaded
shank. The drill must run true within .005 four inchs out .We are having a
hard time holding this tolerance.The drill in the picture is not the one
one we are using the flutes almost touch the threaded shank so
turning the threaded shank after brazing is not going to work.

http://i795.photobucket.com/albums/y...1/DSC00587.jpg
http://i795.photobucket.com/albums/y...1/DSC00586.jpg

We have tried slip fits press fits nothing seems to work.

Were using 4140 hex and the hole runs true with the threads
we can press fit the drill in the shank and it runs true but after
we braze it they run out. Could the materal be the problem?


Has anyone made these before and know how there done.
We only have 5000 to do were in trouble and need help.
Thanks

[bobgerman]

This looks like a job of good old "hand straightening" after brazing. I did this for hundreds of hours many years ago. A pair of v-blocks and a dial (or digital) indicator to show location fo runout with an arbor press to tweak the parts in the right direction. After a few (hundred) pieces you get a (good?) feel for it.

[timlkallam]

This looks like a job of good old "hand straightening" after brazing. I did this for hundreds of hours many years ago. A pair of v-blocks and a dial (or digital) indicator to show location fo runout with an arbor press to tweak the parts in the right direction. After a few (hundred) pieces you get a (good?) feel for it.

A ha, so thats how its done , but these a carbide drills they will break.

Thanks for the reply

[bobgerman]

CNC thread grinding after brazing maybe? Indeed that is some tight work but the beauty of grinding is you can shape the wheel how you want it and it doesn't generate a whole bunch of preasure to distort the work.

[Boltz]

Is it possible rotational friction welding could work for this?

[jimmyblythe]

Good evening,

Old post i know but i was wondering how you managed to solve this? I have some bits i need to make for a project i am working on at home..... And need these to interface to an air motor i have..... Any help would be appreciated?

P.s. How do you measure the run out at the end of a drill?

Many thanks

James

[timlkallam]

Hello James , Brazing the shank on and expecting it to run true never did work.
So now we braze on the shank and then machine it holding the shank
in a collet.

I have found checking for runout is impossible . I machined the female part on the cnc lathe left it in the collet never took it out .
screwed the drill or reamers with the new shanks on them and they just don't turn very true take out the same drill or reamer screw it back in and it runs out in a different place it just does not repet. But keep in mind I an checking the tip and its 4 to 12 inchs away from the shank.

I can put the drill or reamer in a v block and the angle on the threaded shank
will turn within .0002

What i figure is the threaded shank has a 30 dreg. taper per side to center its
self the taper is just to steep and is not a good self centering taper for a drill 4 to 12 inchs long .

We have made alot of these for a large aircraft company and havn't had any complaints .

What i can't understand and I am greatfull for the work, not complaining .is why have a threaded shank on a drill or reamer.

Some or these reamers are 12 inchs long solid carbide coolant thrue
six flute and each flute has a coolant hole to push the chips foward and has a threaded shank.
These reamers are used in some type of machine why not use a collet insted of a threaded shank.?????????

[txcncman]

I have been working in machines shops since 1994. I have never seen an application using a threaded shank drill. I have seen these type drills in several shops I have worked in. I am sure they are a holdover from a time in industry where automation was just beginning and a need for a quick way to change out a tool was needed. At that time in industry CNC was not even heard of. Probably these drills were used at some type of drill press or drilling machine in conjunction with a drill jig plate having drill bushings. Because of the drill bushings to align the drill during the drilling process, run out of the drill was not an issue. Why these drills are still desired by some companies is that they may still be using this older equipment and older methods even today. Companies making parts for the Boeing 737 would be a good example. The 737 first flew in 1967. Parts for the 737 were surely made on the same machines that were making 707's for 1958 and before. Long before NC or CNC. As I said, I have seen these drills in shops I have worked in as recently as this year. They were probably bought at auction, intentionally or as part of a lot. The only way I have seen them used it to walk over to cutoff wheel and whack the hex and thread off and then mount in a chuck or collet.

[jimmyblythe]

I see what you are saying,what type of collet do you hold the shank in? Is it not possible to shrink them in? ↲↲↲on what tools they are used in, i would assume it must be related to a special process? Maybe related to the size of the parts they are working on?

[txcncman]

@jimmy - Actually, you brought up a good point. If you are needing some special type of adapter for certain tooling, you can build said adapters and use heating/cooling to shrink fit the adapters on the tools.

[jimmyblythe]

@jimmy - Actually, you brought up a good point. If you are needing some special type of adapter for certain tooling, you can build said adapters and use heating/cooling to shrink fit the adapters on the tools.

I would assume that cooling the tool down rather than heating the adapter would be preferable?

What type of steel would you use for the holder if you were heating it, is distortion not an issue?

where would i be able to find information on the tolerances?

Many thanks

[txcncman]

I would assume that cooling the tool down rather than heating the adapter would be preferable?

What type of steel would you use for the holder if you were heating it, is distortion not an issue?

where would i be able to find information on the tolerances?

Many thanks

You will probably have to do some of both to get enough clearance to press the tool into the adapter. Expansion and contraction of materials should be available in many engineering books. Maybe even Machinery Handbook. I have not checked and do not recall if it is. Carbide tools will have very little contraction, even at liquid nitrogen temperatures I bet. I do not think distortion will be an issue on the scale we are discussing. Maybe in the 0.0002 range?

I think I might tackle your problem by building a few adapters to fit a collet system and then using collets to fit your various tools.