Pie jaws: 3 jaw chuck or six jaw?

[jools]

Hi all
I have some flat and wide cylinders to machine from Delrin. they're about 165mm (6.5") in diameter and 20mm tall (.75"). I have to machine features on both sides and radial o-ring grooves in the sides too.
I have been using a vac plate but am thinking of using a chuck with pie jaws, or incomplete pie jaws to do the same thing. I have neither a three jaw or six jaw with removable jaws so would need to purchase whichever one I go for.

So questions I have flying round my head are:
- If I go three jaw do I need to clamp the full circumference? Obviously the more the better but is there a point on this thick material where he benefits are outweighed by the cost of pie jaws and maybe having to machine a few?
- If I go six could I use hex bar from brass to again make incomplete jaws but having more points of contact.
- Six jaw chucks are about £800 ish give or take. Three jaw I can get for £150 ish. Ready made pie jaws are £120 a pop. I could maybe make a set of pie jaws for the six jaw for £40.

Which would you guys go for. Is there a major benefit of six over 3 or do I just need a good talking to and to be told to not spend all my money on shiny things.

Cheers
Jools

 

[EmGo]

Hi all
I have some flat and wide cylinders to machine from Delrin. they're about 165mm (6.5") in diameter and 20mm tall (.75").

At 6 1/2" in diameter, 6 jaws will be so far apart that they won't hold for poop without squrshing your delrin. Go with the pies.

Even with a six, I often used three pie jaws for parts like you describe, just left three jaws out. Six jaws are nice but they aren't magic.

 

[jools]

At 6 1/2" in diameter, 6 jaws will be so far apart that they won't hold for poop without squrshing your delrin. Go with the pies.

Even with a six, I often used three pie jaws for parts like you describe, just left three jaws out. Six jaws are nice but they aren't magic.

Sorry I may be guilty of over-explaining in my original post, some call it waffling :-)

If using a 6 jaw chuck I would also make pie jaws. I think my question could be distilled down to:- is there any advantage using a six jaw chuck with pie jaws as oppose to just a three.

My bad
jools

 

[EmGo]

If using a 6 jaw chuck I would also make pie jaws. I think my question could be distilled down to:- is there any advantage using a six jaw chuck with pie jaws as oppose to just a three.

Oh. Well either way pies are very close to full circle. If the parts are really flimsy then you'll get slightly six-sided parts with six pieces of pie, vs three-sided with three. If that's important probably should be front-clamping the parts instead anyhow. If you're making your own, each piece of aluminum is smaller but there's twice as many to make.

Basically, six of one, three of another

 

[Philabuster]

Sorry I may be guilty of over-explaining in my original post, some call it waffling :-)

If using a 6 jaw chuck I would also make pie jaws. I think my question could be distilled down to:- is there any advantage using a six jaw chuck with pie jaws as oppose to just a three.

My bad
jools

There is no advantage to going with a 6 jaw chuck if using pie jaws on a 3 jaw chuck in my opinion.

Go with the 3 jaw chuck and pie jaws. You will likely have to make custom soft jaws for a 6 jaw chuck if you want all 6 jaws used vs just buying off the shelf pie jaws for the 3 jaw chuck.

You can run only 3 regular pie jaws on a 6 jaw chuck. The pie jaws should clear the unused master jaws just fine.

6 jaw chucks have their place, but most of the time a 3 jaw chuck + soft jaws will cover most jobs.

 

[jools]

Oh. Well either way pies are very close to full circle. If the parts are really flimsy then you'll get slightly six-sided parts with six pieces of pie, vs three-sided with three. If that's important probably should be front-clamping the parts instead anyhow. If you're making your own, each piece of aluminum is smaller but there's twice as many to make.

Basically, six of one, three of another

Yeah I thought exactly the same as you, but I also thought a shiny six jaw chuck would be nice. then I thought damn they're offing expensive....... The parts are very sturdy but I just want to be able to put some power through the tool and not mar the part. So I think I'll go with your recommendation and do three jaws and figure out a way to make reasonably priced pie's for it.
Thanks

Jools

 

[jools]

There is no advantage to going with a 6 jaw chuck if using pie jaws on a 3 jaw chuck in my opinion.

Go with the 3 jaw chuck and pie jaws. You will likely have to make custom soft jaws for a 6 jaw chuck if you want all 6 jaws used vs just buying off the shelf pie jaws for the 3 jaw chuck.

You can run only 3 regular pie jaws on a 6 jaw chuck. The pie jaws should clear the unused master jaws just fine.

6 jaw chucks have their place, but most of the time a 3 jaw chuck + soft jaws will cover most jobs.

Cool. Seems the consensus on advice is a three jaw and pies. So that is what I shall do :-)

Cheers

Jools

 

[EmGo]

There is no advantage to going with a 6 jaw chuck if using pie jaws on a 3 jaw chuck in my opinion.

Mostly have to agree with you but there's always some case where ...

On these things

the rings that hold the disks on are so flimsy that even with only 1/8" or so between the jaws, you could measure the out-of-roundness. In this case I just opened the threads a little, and they got chromed anyhow so needed some extra clearance for that so no biggy, but I can see where if you had to be rounder, then maybe six would be better. If six out-of-rounds of half as much as three would get your part through the door ....

On the other hand, front clamping or thread milling would be a better way to do it in that case but don't always have them luxuries

(I already had the 12" six-jaw so wasn't a case of buying it then only using three, mostly ran it with the full 6, in case you're wondering why I am so stupid.)

 

[Mtndew]

is there any advantage using a six jaw chuck with pie jaws as oppose to just a three.

Yes, the 6 pie jaws will weigh half as much.
When you have a 15" chuck they aren't light lol.

 

[jools]

Yes, the 6 pie jaws will weigh half as much.
When you have a 15" chuck they aren't light lol.

But the screws will weigh twice as much ;-)