Joining the Pratt & Whitney 3C family

[SteveM]

I just added my location. Nice lathe. Does that use the 4pn collets? I saw a P&W lathe online somewhere recently but don't recall now. I will have to see if I can find it. I don't need another lathe but who knows.

Of the benchtop models, there are 3 lathes:
Model 3 - uses 3PN collets

Model 3C - 7: lathe, uses 4PN collets

10" bench lathe (not to be confused with the 10" toolmakers lathe) that uses 5PN collets.

Mine is the matching 3C lathe that uses 4PN collets, so I can share them between machines.

Steve

[SteveM]

There's a lathe for sale in New Hampshire, but I can't tell if it's a 7 or a 10:
https://maine.craigslist.org/tls/d/prat ... 65535.html

Has the original speedranger motor on it.

Steve

[discodan]

The one I was looking at is on ebay and is the 3C-7 in your first picture. It has 11 collets, so at $900 that is only $81.81 per collet if that is all you want!

https://www.ebay.com/itm/PRATT-WHITNEY- ... Swa9Fa57Gw

[SteveM]

The one I was looking at is on ebay and is the 3C-7 in your first picture. It has 11 collets, so at $900 that is only $81.81 per collet if that is all you want!

https://www.ebay.com/itm/PRATT-WHITNEY- ... Swa9Fa57Gw

That's the 3, not the 3C (my text is above the pictures, not below).

There is a 10" at or about a grand:
https://www.ebay.com/itm/361760160873?s ... 1438.l2649
but that's 5PN collets.

You can still get collets from Hardinge, but last I saw, they were charging $395 each, so that would be $17,775 for a complete set of fractional. They also came in decimal increments and metric, so a REALLY complete set would be $30,810.

Steve

[discodan]

Steve, I did a little testing today with both collets. With the 4pn and the boring bar there was only 0.001 run-out. I did the same with the R8 and two different end mills and got 0.005 and 0.006 run-out. These were taken within about 1/4" from the collet opening since I couldn't get any farther out on the end mills. I guess I need to think about your prior comments, but this is exactly why I am on here and why I only bought one R8 collet. But frankly, at this point I'm not sure when I will be doing any high-precision milling but it never hurts to be more accurate.

[SteveM]

One of the things I did when I only had one collet (5/8" in my case) was to machine split sleeves in different sizes to put smaller collets in.

Do you have a lathe?

You could chuck up a piece of 1" steel, drill undersize then bore to 1/2" (maybe about 1" deep). You know you have it right when a 1/2" end mill will go in, but you feel the air pressure, and it pops when you pull it out.

Then without removing the piece, turn the outside diameter to 3/4", leaving a small shoulder. The shoulder will prevent it from sliding into the collet.

Then slit the side. You can do that with a slitting saw, or if nothing else, a fine-toothed hacksaw blade.

Here are three commercially made ones (Hardinge) and the one I made. Mine has one slit and it surprisingly accurate. The Hardinge ones are split on opposite sides and from opposite ends (4 splits). You can sometimes pick them up cheap on ebay.

At least with a 3/4" collet, you have a lot of tooling that will fit in it.

Find a drill chuck with a straight-shank 3/4" arbor and cut off the arbor beyond where the collet will grab (makes it easier to install without having to relocate the work). That will give you drilling capability without having to have all the collets in the world.

You can pick up straight-shank end mill holders, but that will give you tool flex with the overhang, but the shank will be 3/4" so maybe not that bad.

Steve

[discodan]

That is a very interesting idea. Do those collet sleeves have a name I can search for? My collet is 3/4" so I could do something similar. I do have a lathe but I haven't tackled anything like that yet but it would be a great learning experience.

I do have one question that has slightly stumped me. My 4pn collet is 3-5/16" but all of the reference material I see says they should be 2.90625". There is no marking on the face. Is that consistent with yours?

Thanks for all of the great info.

[John Hasler]

How are you measuring that collet?

[SteveM]

Do your collets look like this:



Steve

[discodan]

In general yes. I am not at home to take a pic but mine have a flat face instead of the rounded face and the transition from the taper to the face is a little less than 1/8" and is parallel to the body of the collet. Your picture looks like there is no flat transition like I have. When I measured my collet I measure the entire thing from end to end, including the 1/8" transition. In the charts I see online they don't include the rounded face in the measurement but mine is a flat face. As I noted before I can't see any markings on the face but the face is narrow and has wear on it so it may have been there but lost to time and use.

[discodan]

Here are two pics of the collet, so you can see how long it is, not including the flat transition between taper and face. After putting a flat edge on the face it does have a slight crown to it.

[SteveM]

The overall length of mine is about 3" and the length from the threaded end to the start of the taper is about 2-1/2".

My guess is that yours is homemade.

Steve