Rc 45-50

I want to turn down the shank on a fly cutter from 3/4 to 1/2 inch so that it will fit in my mill. The manufacturer says that the hardness of the shank is Rc 45 - 50. I have been trying to find out what this means, but the information on the internet is confusing.

What I would like to know is: can this be turned on a lathe with a carbide tool insert? I have no idea what this rating equates to.

Thanks, John.

Suck it and see

Stick it into the chuck, and if possible, use a tailstock centre to get better stiffness/accuracy.

Thanks for the advice. The problem is I haven't purchased the cutter yet and don't plan to if I find out that I won't be able to machine it. I could purchase a smaller shanked cutter, but I really like the one with the 3/4 shank. John

Carbide cuts most metal, the "harder" metals are usually up in the 60s

link

With tuff jobs backgear speeds can sometimes be better than high speed turning, high speed stuff can sometimes become a tool grinding exercise.

Edited By Ady1 on 10/08/2016 01:54:10

I will have a guess and say the 3/4 shank has a larger swing on the cutter than the 1/2 shank ?

If so turning down to a smaller diameter could cause it to flex more - not what you want on a flycutter.

I hope you are not wanting to turn down the shaft so it fits in a drill chuck as it will end in tears !

Maybe be easier to get the correct collet for it .

Carbide will cut it although getting a good finish maybe a chore , it is possibly case hardened and ground to size .

One problem can be if your finished size is right where the case hardening finishes as there can be spots with case hardening and spots without , the tool will skid on the hard stuff but cut the soft stuff and it will end up out of round and not parrallel probably not a problem when you want to remove 1/4 on the diameter.

45-50 rc is the hardness on the Rockwell scale of hardness , google Rockwell hardnes scale and you should find the info easily enough.

Ian

Rc 45-50 equates roughly (and these things are always approximations) to a tensile strength range of 95-115 Tsi, or 215-255 Ksi, or 1460-1740 MPa, so at the higher end of what you are likely to come across.

There are plenty of hardness conversion tables available out there - they will vary somewhat in the numbers they give.

Tungsten carbide tools will cut to Rc 65 . Run the surface speed at 25 to 35 m/min So basically in your case you should be able to turn it at about 400 to 500 rpm, take cuts from 0.1 to 0.3 mm deep, about Ø0.2 to Ø0.6 mm cuts, and a feedrate of 0.05 to 0.08 mm per rev, basically 2 to 3 thou per rev. If you use ceramic inserts you need a lot more rpm's and flood coolant. The gold coated carbide works well so does the newer vapour coated insert like the VP15TF coated inserts from Mitsubishi. That will give you a coating comparison to work with.

Neil

I note you gave much more inf

o on another forum. I would not recommend reducing tool dimensions without very good reason. Later overloading of the machine or tool is one risk, often forgotten after the initial change. Prolly not applicable to this machine-tool combination, but people do change machines....

With regard to hardness, the Rockwell scale is one of several and relates to the ability of the surface to resist abrasion, surface denting, etc. Generally, the harder the material, the less resilient the object is to bending - really hard offerings of the same material will be brittle at high hardness - tools/items can easily shatter if struck too

hard. There needs to be a balance between hardness and flexibility for most items, dependent on application. Shanks are often hardened to avoid damage from chucking.

Go with carbide for easy turning, but surface finish is important and may be a problem. XD351 is likely spot on the money. Using tools too big for the machine is attractive, but not necessarily a good move. Reme

mber, by reducing the diameter by 33% means removing more than half the metal in the shank....

In my experiments turning hardened steel (>65Rc) I got an excellent finish, about 1µm Ra with a carbide insert. One needs high surface speed (>100m/min), shallow depth of cut (~0.2mm DOC) and reasonable feedrates (>0.1mm/rev). Ideally the metal in the shear zone is at least red hot and hence relatively soft.

Andrew

Just don't use a Jacobs Chuck to hold the finished tool in the mill, it needs a collet of some sort with a draw bar to hold it in place.

Ian S C

After listening to the voices of reason, I decided to go with a cutter that has a 1/2 inch shank and avoid all of the problems that were pointed out to me. Thanks for all of the great advice, John.

How will you hold it John? When I first got a mill in the mid 90s I knew nothing of mills, and draw bars, or what a milling cutter should look like, so I stuck a 1/4" end mill in the Jacobs chuck, and it worked quite well---for about 2 minutes, then the chuck fell out. I still have, and use the tap wrench I was making, with a chunk out of the side to remind me.

Ian S C

Ian,

My mill takes 2VB collets, and I have a full set of them up to 1/2 inch. The spindle will not accept any thing larger so the question of turning down the shank.

Thanks for your concern. John