What Size Drill and Tap To Use?

[ml_woy]

I am in the process of building a ball turning attachment for my lathe and have decided to use a carbide insert as my cutting tool. I am about to attach the insert to the tool post however I am in a quandary as to what size drill and tap to use to secure it to the post. The diameter if the hole in the insert is .140", any suggestions?

[PixMan]

Just what is the designation of the insert? Is it a countersunk hole?

To have the insert fastened secrurely and prevent any movement, you need to carefully put the hole in the right place relative to the hole in the insert so that the screw pulls it snugly up against the pocket shoulder. If you give me the insert nomenclature I can give you all the information you need to make it a good holder.

[ml_woy]

(01-02-2013, 09:15 PM)PixMan Wrote: Just what is the designation of the insert? Is it a countersunk hole?

To have the insert fastened secrurely and prevent any movement, you need to carefully put the hole in the right place relative to the hole in the insert so that the screw pulls it snugly up against the pocket shoulder. If you give me the insert nomenclature I can give you all the information you need to make it a good holder.

The insert I am using is a TNMG-321
I.C. 3/8"
Thickness 1/8"
Radius: 1/64"

The top of my tool holder is 3/4" x 1.06" and I was planning on mounting two inserts back to back with a .125" wall in the center separating them. In that way I could use the tool to do inside and outside radius's.

Another forum member recommended the use of this fastener http://www.use-enco.com/CGI/INSRIT?PMAKA=250-1299

[Arbalest]

I used a countersunk screw with the head turned down a little on mine.



For this particular insert I used M4.

[EdK]

(01-03-2013, 01:18 PM)Arbalest Wrote: I used a countersunk screw with the head turned down a little on mine.

For this particular insert I used M4.

Very nice ball turner.

Ed

[Arbalest]

Thanks Ed. like some other folks I fitted a ball race between the two major parts to make it nice and smooth in use.

[stevec]

Arbalest, neat looking ball turner. Are the insertseat (dark grey), slide & base (Medium grey) & turret 7 handle (alu. color) different metals? if yes, what mat'ls and why. Does the base bolt to the t slots in your X table and can you leave your compound in place while using the ball turner?

[Arbalest]

Hi Steve,

All parts are steel except the ball which is alloy. The rest of the handle is stainless. Just stuff I had in the stock "bin". The rotating part is pretty much as turned but the other parts are sand blasted. Sadly I don't have T slots on my BV20 lathe so I had to drill and tap the cross slide. The top slide has to be removed but it only takes a minute. In case you're wondering, the bearing I used is 42mm OD, 15mm ID and 13mm thick - again, just what I had in stock. Don't ask me what the insert designation is, I just bought a couple at a model engineering show! Hope this helps.

[PixMan]

(01-03-2013, 10:05 AM)ml_woy Wrote: The insert I am using is a TNMG-321
I.C. 3/8"
Thickness 1/8"
Radius: 1/64"

The top of my tool holder is 3/4" x 1.06" and I was planning on mounting two inserts back to back with a .125" wall in the center separating them. In that way I could use the tool to do inside and outside radius's.

Another forum member recommended the use of this fastener http://www.use-enco.com/CGI/INSRIT?PMAKA=250-1299

A negative rake insert like that should be using and eccentric screw in the middle and a top clamp to secure it, just as most negative rake insert toolholders would have. I suppose you'd be OK with a #6-32UN screw (nominal O.D. = .138") but only of you're very gentle with the cuts or have the 2 non-cutting corners of the insert capured to keep it from moving while taking a heavier cut. Looking at the screw recommended on Enco's site, I'd be wondering where to get an M2.2 x 0.45 tap for it and how much would the tap cost?

If I were making a ball cutter using an insert, I'd choose a VBGT331 or similar. That way I would mill the pocket with a 5º per side (10º included angle) cutter to mill the pocket, put the tapped hole in at a position .002" closer to the walls of the pocket so the screw woould pull it into the pocket snug (just like all commercially made holders do.)

[sasquatch]

Yes, very impressive ball turner!!