Taper pipe plugs for expanding fixtures?

[Garwood]

I've built a few fixtures using the Mitee Bite XYZ expanding pins. They work decent, but I'd like a lower cost/simpler alternative for low volume fixtures.

I've used pipe plugs to expand shafts before in assemblies and I built part of a fixture where the pipe plug permanently expanded to lock parts together.

Anyone use them in fixtures? I'm looking at a part right now that I sell 20 of a year. I'd like the grip the inside of a 1" counterbore on the flip using a pipe plug expanding boss. I've traditionally made them in a double vise. I use a heavy chamfer on one side to remove the .100" lip left from milling the part in serrated step jaws.

I'd rather make a cheap dedicated fixture than deal with setting up a vise, getting the right jaws, setting the correct work stops, etc. I also can't fit a 6" double vise in my 400MM HMC. But if I make a fixture I can run that fixture in any machine I have.

Anyone had problems using NPT plugs to expand a boss in a fixture?

 

[Mud]

I've done it, worked fine. For quicker and dirtier I've used a taper tap run in shallow and used a straight set screw to expand. I think the pipe plug is better.
To hold pistons by the wrist pin hole I made a mandrel, drilled and tapped it for 1/2-20, chamfered the end of the hole at 45° then turned the underside of a SHCS to 45° to match, slit it crosswise on a bandsaw. First one I sawed the slits too long, and I could grab the piston and rock it around the solid part of the mandrel, flexing the slit portion slightly. Still worked fine for flycutting valve reliefs.

 

[Pmtool]

Some ideas here perhaps. Rovi products. I have used expanding id chucks on lathes a lot.

Rovi products

 

[vmipacman]

When I did it I made sure to tap NPS threads. NPS threads with the tapered plug probably gave me more spread.

 

[Barbter]

I've never seen it done, and never even thought to do it....but used plenty of standard cap heads, and machined a 60deg taper (cone) on the head which works well.

 

[lobust]

I've never seen it done, and never even thought to do it....but used plenty of standard cap heads, and machined a 60deg taper (cone) on the head which works well.

That's how I've done it too, have quite a lot of fixtures that work around that principle

At the same time, I have used the forcing a plain screw in to a not fully tapped hole method in times of need... It works, just not quite as well and for not quite as long!

 

[mach ramsey mn]

Looking at the Mitee bite product you would need p/n 312500, MSC is list at $56. My thought process is can you build this for $56? The next question is can you replace it for $56? Just labor I don’t think most guys could do this in under 2 hours deburred and all.
Just this man’s perspective.

 

[Garwood]

Looking at the Mitee bite product you would need p/n 312500, MSC is list at $56. My thought process is can you build this for $56? The next question is can you replace it for $56? Just labor I don’t think most guys could do this in under 2 hours deburred and all.
Just this man’s perspective.

No, I'm not building that. I have a shitload of rem 1.25" 6061 plate from the parts I make. I would start with a chunk of that. Mill away what isn't four .5" tall .900" bosses. Drill and tap 3/8" NPT in the bosses. Mill three 1/4" wide slots for the boss to expand and mill a slot around the boss, probably an additional 1/4" deep to alloow the boss to flex better.

I can model that up, cam the program, setup the mill and cut that in about 1.5 hrs tops.

 

[Garwood]

I've never seen it done, and never even thought to do it....but used plenty of standard cap heads, and machined a 60deg taper (cone) on the head which works well.

Definitely hear you on the SHCS. Only dilemma with that and the cheap, quick and dirty 2nd op fixture is the height of the SHCS would require a thicker fixture plate or locating the bosses over t-slots which would I could do.

I'm gonna give a super cheap $0 aluminum and pipe plug fixture a go and see what happens.

 

[Spruewell]

It would be interesting to know how may cycles you get before the threads start to gall in the aluminum. Maybe a dab of Moly on there would be helpful.

 

[Garwood]

It would be interesting to know how may cycles you get before the threads start to gall in the aluminum. Maybe a dab of Moly on there would be helpful.

Same thought. I was thinking somebody might say they tried this and they only got 6 parts before it went to shit. In that case, it wouldn't be worth it.

Maybe with some antiseize on the threads and running with npt's with a low torque setting on a screwdriver they might stay alive for awhile.

 

[Mud]

Definitely hear you on the SHCS. Only dilemma with that and the cheap, quick and dirty 2nd op fixture is the height of the SHCS would require a thicker fixture plate or locating the bosses over t-slots which would I could do.

Ever use allen nuts? A FHCS up from the bottom with 2 threads to hold it in place and a tapered allen nut on the top might work. Metric flatheads are 100° which makes them shallower. Or low head socketheads mebbe. Or a plain stud/setscrew.

 

[mach ramsey mn]

Ever use allen nuts? A FHCS up from the bottom with 2 threads to hold it in place and a tapered allen nut on the top might work. Metric flatheads are 100° which makes them shallower. Or low head socketheads mebbe. Or a plain stud/setscrew.

View attachment 3755

Pretty sure metric flat heads are 90 degrees.

 

[Mud]

Pretty sure metric flat heads are 90 degrees.

OK, I think you are right. What is 100 then? I forget. Something aircraft maybe.

 

[mach ramsey mn]

I think aircraft rivets? Got hung out on 82 degree chamfers on metric screws once… only once,

The Google says flathead aircraft rivets are 100 degrees…

 

[Mud]

I did a firewall/block plate for a scattershield that specified 3/8 100° flatheads, I didn't provide the fasteners so don't know the specs of the screws. Googling turns up small ones. 1/4 and under.

 

[mach ramsey mn]

SAE is about take your pick of angle…

 

[MwTech Inc]

mc M has these
rolled threads, stainless steel
the aluminum may like these a lot better than an old rough iron plug........

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

 

[Spruewell]

Oh, no! Stainless threading into aluminum? You are definitely asking for problems. I don't recall the exact reasons, but stainless will gall in Aluminum really bad.

 

[mach ramsey mn]

It’s a galvanic reaction, a little battery swapping electrons around doing some slow welding!
I don’t know why it is but the packaging machine builders around here love to have stainless fasteners in all of the aluminum parts. I’ve been told they think they are stronger than standard shcs….