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Positioning bushes for welding

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sparky mike17/11/2019 11:01:39
196 forum posts
50 photos

I have to weld two 1" diameter steel bushes into two holes in a steel 3mm plate. How can I jig these up to be spot on square to the plate? They are not flush with the plate but protrude around 3/8" on the back side.

Mike.

pgk pgk17/11/2019 11:08:38
1486 forum posts
285 photos

The obvious answer would be a 3/8ths cup on the back and 3/8th supports or tack from the back if flush at the front. But I guess there's a reason why you can't do that. Won't the bushes get distorted anyway? Can you not weld some plugs and machine them out afterwards? Or rely on locktite?

pgk

ega17/11/2019 11:09:26
1335 forum posts
109 photos

I would tack them, check, adjust as necessary and then finish weld.

Daniel17/11/2019 12:09:49
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254 forum posts
39 photos

+1 to ega's post.

Tack weld, adjust to final position, finish weld;

ATB,

Daniel

sparky mike17/11/2019 13:17:02
196 forum posts
50 photos

It has to very accurate so think this is the way I am going.

Thanks for replies anyway.

Mike.

sparky mike17/11/2019 13:19:51
196 forum posts
50 photos

Photodocument1.jpg

Martin Connelly17/11/2019 13:29:43
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893 forum posts
111 photos

Welding and accuracy are somewhat mutually incompatible. The weld pool freezes at a high temperature and all the way from freezing to room temperature it is contracting and creating stresses. These stresses will distort the fabrication to some extent. Fabrications for tools and jigs have to be stress relieved after welding and before machining as a result. No matter how accurately you position them for welding expect some movement away from the ideal position.

Martin C

Dave Halford17/11/2019 14:26:23
489 forum posts
4 photos

treat each bush as a compass.

Scribe the bush with the position of the plate

tack north, then south, then east, then west, like torqueing up a cylinder head.

Check the scribed line after each weld and adjust as required.

Your bridge is quite flexible so still expect some movement.

Nicholas Farr17/11/2019 15:06:21
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1997 forum posts
956 photos

Hi Mike, can you not turn a the end of the outside of the bush the required length and put in a smaller hole?

You will not stop distortion, no matter what you do, but it can be controlled by slight bowing of the plate before welding, but of course you will need some experience before you are able to do this satisfactory.

Regards Nick.

sparky mike17/11/2019 16:57:16
196 forum posts
50 photos

I made the simple jig, but instead of two welded legs to the bridge, I tapped the top plate and now have two 3/8" unf long threaded bolts in. I had thought about having each end of the bushes with turned spigots, but plate holes were in before I got to thinking on a bit.

Mike.

Brian Oldford17/11/2019 17:33:30
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582 forum posts
4 photos

Weld in pieces of rod that have only been centre drilled. Weld into the plate getting them as square as possible the drill through with a mag drill.

Dave Halford17/11/2019 17:50:49
489 forum posts
4 photos
Posted by sparky mike on 17/11/2019 16:57:16:

I made the simple jig, but instead of two welded legs to the bridge, I tapped the top plate and now have two 3/8" unf long threaded bolts in. I had thought about having each end of the bushes with turned spigots, but plate holes were in before I got to thinking on a bit.

Mike.

You could weld a ring around each bush then turn that down to form a shoulder

John Reese17/11/2019 18:19:41
799 forum posts

My preference would be a bush with a shoulder on the OD to set depth and squareness.

sparky mike17/11/2019 20:53:26
196 forum posts
50 photos

Hi John,

A solid round piece of bar , counter bored to the depth of the bush overhang and a good fit on the o/d of the bush, in conjunction with my jig on the other end should work well. Hope for a warmish day in the workshop tomorrow !!

Mike.

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