Thread: Cutting accurate angles in RHS

How are you cutting the old/rusted material out.

What ever method you use to accurately mark the cut on the rusted piece just use that on the new piece,this assumes that you are cutting the old piece out in situ and not mounting the boat trailer chassis on some type of saw.

Its horses for courses.

The outcome hinges on
* Your friction saw - what brand is it? How it is mounted
* The quality of the friction wheels.
* the dimension of the section being cut.
* The way the saw is used - let the revs cut the steel so it is not forced- less likely to deflect the wheel.
* Change the wheel when its needed- pushing the bejesus out of a worn down wheel makes them run off bigtime.

I think if you follow the suggestions about improving the rigidity of the saw base it will help immensely.Do test cuts on the dimension material you intend to cut and check for the deflection.
Also what was not touched on, was the friction wheels themselves. By cheap and deserve what you get .Spend a little bit and the situation improves.I found Makita friction saw blades did a very good job ,so long as the not pushed too hard.

I used Makita friction wheels on my my GMC saw which I still have. It is mounted on a castored trolley with support fore and aft to support the weight of the stock to be cut.

For the marking out I use a very narrow point ink maker.

Hope it helps

Grahame

Thanks for the replies and advice guys, it is truly appreciated.

Have attached a few pics below of what I'd like to recreate. The whole part is separate from the rest of the trailer and basically bolts on.

You can see some of the angles I'll be trying to cut, which is my main concern. IMG_20170614_163516726.jpgIMG_20170614_163509124.jpgIMG_20170614_163449632.jpgIMG_20170614_163439986.jpg

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That's not actually a simple repair - the beams you are looking at have been hot dip galvanised and look to have reinforcement pieces on the angles so could be structural in their nature.

Michael

Yeah, I don't actually want to repair but rather replace. That while piece is separate to the rest of the trailer, so wanted to fabricate a whole new undercarriage

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garfield,

Easy peasy if you have a layout(welding) table of sufficient length.

Even a bit of sacrificial plywood is even good enough to layout all the angles.

Once tack welded, I would tack on braces to stop the weld distorting the angles( pulling them out of alignment )

Once welded ,a good move is to get the piece double dip galvanised.

Grahame

Thanks for the advice Grahame.

Mate, I was thinking of buying pre gal and cleaning off the gal where needed for welding, and just spraying cold gal over he welds once finished... What do you think mate?

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Originally Posted by garfield

Thanks for the advice Grahame.

Mate, I was thinking of buying pre gal and cleaning off the gal where needed for welding, and just spraying cold gal over he welds once finished... What do you think mate?

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I don't have a lot of faith in the duragal or pre gal sections.
Try a bit in salt water and see how long the coating lasts.It is not dipped ,but plated on and is very thin.

I have a couple and have found that the guy who drilled the frame for the pivot was high on one side and the saw would not cut square so made a couple of bushes and bored the frame so that the holes were parallel to the base .
And now a 90 degree cut is very close not 10 degrees out .

Michael

You're right about gal. If you look at the specifications even hot dip gal is not suitable in a salt water environment as a builder on the coast found out the court ordered a marine paint system had to be used on exposed hot dip gal beams. In your case it would be overkill but if exposed to salt water regular inspection would be advised.

Yeah, ideally if I was good enough I'd make the whole undercarriage the way it is out of c-purlins so nothing was enclosed band I could wash it all out after ever dip.

That's why I thought if I used the pre gal and closed all the ends off so the salt water couldn't get in I'd just do it that way and if it last 5 or 6 years plus I'd be happy with that

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Originally Posted by garfield

Yeah, ideally if I was good enough I'd make the whole undercarriage

Don't be so hard on yourself mate!

I am sure with a bit of tweaking of your drop saw ,you and your saw will be good enough.

To confirm to myself the process is possible, I have just been up the back and used the 14' GMC to cut some 50 x 25mm x 1.6 SHS,which is about as close as I have, to the 45 x 45mm your part looks to be made from.

I first cleaned up the deck. When you put your friction saw away dirty all, of the steel particles on the deck congeal into a rusty mess which will throw the alignment of stock to the friction blade -off .

I then squared the vice protractor to the friction wheel with a square. The resulting 90 degree cut both ways is dead square bang on-no light at all under the blade of the square used to check it- in both planes.
The thing is to take care that minimum pressure was used to make the cut.

I would set the saw up up on bench .Working off the floor can only lead to inaccuracies in my opinion. If you aren't comfortable you can't work well.

If I can find my camera I'll take a piccy.

Grahame

Found camera.

Took piccy.

50mm side dead square.jpg

Thanks Grahame, you're a great man!

Don't know if you remember but you helped me through welding for the first time when I made some legs for a camp kitchen.

I'm gonna pull my Ryobi saw out and have a play with it and see if I can get it cutting straight and vertical.

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Those bends are probably formed by a pie cut?