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Fixturing round parts

gking86

Plastic
Joined
Nov 3, 2016
Location
Southern Illinois
I have several types of parts that are round that I would like to come up with a new way to fixture. The parts are thread splits and striker plates for Stretch Blow Molding. They get wired in half, and usually they are stuck to a large magnet which is set against 123 Blocks on the table. This generally gets the job done, however it means that my upper and lower flush cups are almost as far apart as they can possibly be, and the wire runs through a bit of steel, then an 1-4" of open space then more steel. Wire almost always breaks in the lower portion where flushing is poor.

I'd like to turn the parts so that I am cutting through the solid part with no gaps. This would also let me get my Z axis a ton shorter. The parts never come through with the same bolt pattern twice. I'll do 20 or so with a pattern and then never see that set up again. They do have the same specs on the bolt holes and counterbores, so I've turned pins that fit tightly in the holes. Attached is a rough wireframe of what I think would work.

wireframe.jpg

The idea is to set one to the table and use taper pins or something to locate it the same place every time. The second part is going to have holes drilled and tapped and I'm going to run some real fine threaded rod through both of them and use that to adjust the "soft jaw" until it indicates in to my X axis. I want to mill out a half-slot on the face of each that the pins will set in. I'll find center off of the jaws of this fixture and just wire across the table in X+. In my mind, as long as the fixture is indicated in parallel to X and the parts are in tight, I should be able to cut them consistently in spec.

I hope this makes sense. I can get some photos here shortly, but we have a no-cellphone policy and zero signal anyway. So whatever photos I take will have to wait till tonight.
 
No idea what you are trying to explain. What diameter are your parts? Lobster claw or V block are most common ways to hold round parts. Google 3r lobster claw.
 
No idea what you are trying to explain. What diameter are your parts? Lobster claw or V block are most common ways to hold round parts. Google 3r lobster claw.

So, pictured below is roughly the setup I want to go to and the setup I am on. Currently I am aligning parts on a big magnet and cutting them in half. The diameter of the parts is never the same, but anywhere between around 2-10". The ones I'm showing are pretty average. I want to go to some sort of rail system that spans the table where I can align and cut a line of threads without going through the part, open air, then the part again.

In these photos, the rule represents the wire.

Currently using this magnet:
20161229_135400[2].jpg

Want to go to some sort of table-spanning vice holding the parts with pins:
20161229_135826[1].jpg
 
Why are you making it so complicated?

Flat plate with a pair of dowel pins, some tapped holes, and a start hole.

"Vee" the part in the dowels, clamp it to the plate, and split it.

If you split it "between' the dowels your center-line won't change with part diameter.

No muss, no fuss.

When your done with it you take the whole thing out and put it on a shelf 'til next time ...

... and you don't have two dozen parts to round up every time you want to use it.
 
I would guess the holes in the flange of the part need to be timed to the wire cut? If so, just bumping it into two dowels probably won't work...

Josh

Sent from my XT1093 using Tapatalk
 
I would guess the holes in the flange of the part need to be timed to the wire cut? If so, just bumping it into two dowels probably won't work...

Josh

Sent from my XT1093 using Tapatalk

Yeah, the split must go down a line midway between some of the holes. To complicate it further, sometimes flats are cut in the sides so I can't just use a V block. Setting pins in the holes in the parts themselves are the only way I can think of to make it universal.
 
Provided you always have two opposing holes, you could mill slots on your two rails with a slip fit for the pins. Place the part on the rails, drop pins through the holes into the slots, clamp down if you need to and that's it. Won't work if the holes aren't always symmetrical though.

Josh

Sent from my XT1093 using Tapatalk
 
Provided you always have two opposing holes, you could mill slots on your two rails with a slip fit for the pins. Place the part on the rails, drop pins through the holes into the slots, clamp down if you need to and that's it. Won't work if the holes aren't always symmetrical though.

Josh

Sent from my XT1093 using Tapatalk

Same thing would work with a single plate.
 
If the bolt pattern is the same from part to part, how about shoulder bolts. Clamp and locate in one go.
 
20170306_133057.jpg

This actually worked out better than I expected. Milled a shelf and tapped some holes in some scrap (that's why there are so many random holes and "features." Shelves are within .0003 over the length. The holes were having some issues, so I ended up "clamping" on the OD and using a square to line them up. Parts all come out within the .005 tolerance and these wire about 4x faster than the way we previously wired them. My cycle time on four of these (fairly typical) thread splits came out to right at 1 hour, when it used to be 40min-1 hour per part. Haven't tried speeding them up yet.

EDIT: You'll have to forgive my dirty machines, these particular parts were pretty nasty and the photo is from the end of the day.
 
View attachment 193100

This actually worked out better than I expected. Milled a shelf and tapped some holes in some scrap (that's why there are so many random holes and "features." Shelves are within .0003 over the length. The holes were having some issues, so I ended up "clamping" on the OD and using a square to line them up. Parts all come out within the .005 tolerance and these wire about 4x faster than the way we previously wired them. My cycle time on four of these (fairly typical) thread splits came out to right at 1 hour, when it used to be 40min-1 hour per part. Haven't tried speeding them up yet.

EDIT: You'll have to forgive my dirty machines, these particular parts were pretty nasty and the photo is from the end of the day.

Did you drop pins into the mounting holes to set alignment and rotation at the same time with the square?
 
If you have parts like those in the photos, could you just "align" one part and push them all together against the flats?

PM
 








 
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