Fixtures, trunions, welding and truing on the lathe

[Cat Whisperer]

I've just welded up the ugliest set of trunnions on a mini-cannon I've ever done.  Got them well aligned by eye and clamped, welding was OK but not good in that I was putting too much material into it (wire welder).  [I HAVE got to get a TIG welder!]

So, being satisfied with the process for locating the trunnions (7/16 ddiameteron a 7/8" diameter tube), and having way too much weld metal, I chucked up the tube in a 4 jaw chuck to see if I could trim the trunnions back to the tube.

It almost worked.  I had ground a lot of material off, so locating with a dial indicator was a little faulty.  The turning went well, but location was not exactly right.  

So, I'm planning a fixture to hold the tube onto a faceplate, where the fixture can be rolled over 180 degrees to correctly locate the center line of each trunnion better.  That will do for smaller tubes on the lathe, but larger ones are another story.

Pictures - no way!  Far too ugly.  Pictures when I get something that works better.

[GGaskill]

I don't quite understand what you are doing here; machining the trunnion itself?  Maybe make a fixture for the cross-slide to hold the barrel and put an offset boring bar in the headstock.  Should be able to turn trunnions for any barrel you can make with the lathe.

[Cat Whisperer]

I don't quite understand what you are doing here; machining the trunnion itself?  Maybe make a fixture for the cross-slide to hold the barrel and put an offset boring bar in the headstock.  Should be able to turn trunnions for any barrel you can make with the lathe.

Good idea.  Building a fixture to hold a tube should be straight forward.

[gary michie]

HI
Do you have a boreing head for your mill?
    Put your tube on the mill, trunnion vertical to the bed parallel to the spindle. install the boreing head with the cutter installed inward instead of outward and work inward to the diameter you wish.
     gary

I do, I'd been putting off building the fixture that will hole the tube.
I've accumulated a bunch of material, so it's time to do some design work.
The only part I've been wrastling with is how to rotate the tube exactly 180 degrees to precisely locate the second trunion with the first.

[gary michie]

HI
Do you have a boreing head for your mill?
    Put your tube on the mill, trunnion vertical to the bed parallel to the spindle. install the boreing head with the cutter installed inward instead of outward and work inward to the diameter you wish.
     gary

I do, I'd been putting off building the fixture that will hole the tube.
I've accumulated a bunch of material, so it's time to do some design work.
The only part I've been wrastling with is how to rotate the tube exactly 180 degrees to precisely locate the second trunnion with the first.

   Does either trunnion have alot of good surface???
   In a thick plate, drill/bore a hole(a deep hole) that will press fit that trunnion, bolt the plate to the bed, center on the top trunnion by sweaping it with a dial gage (make sure the rest of the tube is blocked up well frist) and with a little luck you have got it. Now how sure are you that the trunnions are 180 degrees from each other in the first place??? My eye ball doesn't work very offend, you may want to sweep the trunnion up high and low and make it parralle to the spindle only.
gary

[Cat Whisperer]

I'm starting with a piece of steel for a base (3/4 or so thick) about 6" wide and about 24" long.  I'll have two places to locate to the milling table with 1/2" wide 'cleats' (for lack of the real name).  I do want to be able to adjust +/- 15 to 30 degrees to be able to cut tapers too.  On top of this will go the fixturing to hold the tube.  First thought is a choice or combination of V-blocks and/or centers.  Both should be adjustable for height.  These also should be adjustable for distance between - to accomodate a wide variety of tubes.  That's the start of the plan.

[GGaskill]

Having built and used a milling fixture to turn trunnions on a rotary table on a Bridgeport,  I would say that V-blocks are better than centers because you can more easily clamp the tube to prevent rotation about the tube axis.

[Cat Whisperer]

Good.  Thanks, I'll have questions of clamping methods soon.

I dug out my 1/2 x 6 x 24 ir'n plate for the base.  Already notched on the ends to bolt down.  Need to put on two cleats for allignment.

Found a 4x3x3 (aprox) pair of Vblocks bolted onto a 1 x 4 x 16 steel plate - adjustable to several positions by rebolting with 1/4-20 AHCS's.  (An e-bay purchase a few years ago.)

Now to swivel one end and put a scale of offset degrees on the other.  (Copying the idea from one of y'all who posted a picture of it - THANKS!)

One step at a time.

[Powder keg]

Going to get all fancy with a scale and all :grin:  Good. I made the swivel in the middle so I could get more travel.

[Cat Whisperer]

Going to get all fancy with a scale and all :grin:  Good. I made the swivel in the middle so I could get more travel.

Excellent on two counts, that leaves the ends open for clamping.

[GGaskill]

You might consider narrower and soft material V-blocks since usually you will be holding tapered pieces which won't sit flush in a wide V-block unless the block can tilt relative to the base.

[kappullen]

Here's how I bored one pattern for the trunnion holes.
I put wooden vee blocks between the angle plate and pattern and held with a couple of c clamps.
This is set up between centers on the mill.
A couple of rough sawed aluminum v blocks would work here.



Here's how I did the tube. I used a hog mill and milled it in light cuts.
The mill is set so it will push the trunnion away from the mill if a bite in happons. I finished off the hog mill marks with a file.




It all depends on what you have to work with and are familiar with.
The Vee blocks with a boring head would do fine too.

Kap

[Cat Whisperer]

Ahhhh MORE great ideas.

Right now it's one small step at time.

I'm looking at using a 1" diameter rod to swing the two parts of the fixture (1/2x6x24 base under 1x4x16 v-block base).  Toying with the idea of using a sleave on top of the 1" rod to locate to the first trunnion spot face to ensure 180 degree rotation and location for cutting the 2nd spot face.  I have a LOT of 1-7/8 dia rounds - so I could custom cut one for each different barrel.  After that gets built I'll consider adjustments/position etc. of the v-blocks and/or centers.

Kap - I have an index head of about the size of yours - a lot of steel to move around!