interestedparty
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| posted on 24/11/02 at 08:26 PM |
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Marking and cutting compound angles in RHS
My chassis design calls for a number of plates (subframe brackets and suspension towers) to be joined by rhs. Trouble is, these plates are not in the
same plane and not even in parallel planes. To join them neatly I need to cut a compound angle on each end, and the correct distance apart.
Once I have the steel marked I can cut it OK, the problem is, how to mark it reasonably accurately bearing in mind that I can't put the tube into
position until it is already cut to the right length and angle, or, more likely, shorter than the right length!
I have tried measuring each of the two angles involved (at each end) and setting those angles up on my cutting equipment and that can work reasonably
well but only on angles of maybe 30 degrees (where a right angle cut would be 0 degrees). After that the blade tries to slide down the side of the
material instead of cutting into it.
What would be really great would be is if I could accurately mark the RHS with felt tip etc and then rough cut it with a hacksaw, then finish it with
a hand held angle grinder, simply removing the material above the mark. I've experimented with this, holding one end next to the plate and marking
the lines by eye, but I've been unable to get to within the tolerances allowed by filling gaps with weld.
Any ideas anybody?
John
As some day it may happen that a victim must be found,
I've got a little list-- I've got a little list
Of society offenders who might well be underground,
And who never would be missed-- who never would be missed!
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chrisg
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| posted on 24/11/02 at 08:32 PM |
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Hi John,
What about a "dummy" length of the right size made from thin card? This could be offered up to the plate and trimmed to get a good fit then opened
out and wrapped round the rhs to mark it.
Card's easier to cut than rhs!
Cheers
Chris
Note to all: I really don't know when to leave well alone. I tried to get clever with the mods, then when they gave me a lifeline to see the
error of my ways, I tried to incite more trouble via u2u. So now I'm banned, never to return again. They should have done it years ago!
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interestedparty
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| posted on 24/11/02 at 08:50 PM |
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quote:
Originally posted by chrisg
What about a "dummy" length of the right size made from thin card? This could be offered up to the plate and trimmed to get a good fit then opened
out and wrapped round the rhs to mark it.
I quite liked this idea, Chris, and I can certainly see me using it in some situations. It won't help this time, though, because the distances are
400-700mm and the technique would require to me to make in effect a card tube which would bend while I was trying to mark it. Over a shorter distance
I reckon it would be OK
Thanks
John
As some day it may happen that a victim must be found,
I've got a little list-- I've got a little list
Of society offenders who might well be underground,
And who never would be missed-- who never would be missed!
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Wadders
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| posted on 24/11/02 at 08:58 PM |
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What about a "dummy" length of the right size made from thin card? This could be offered up to the plate and trimmed to get a good fit then opened
out and wrapped round the rhs to mark it.
Card's easier to cut than rhs!
Quite right Chris,what your describing is a
facet of technical drawing called"developement" or in simple terms "templating". Its used all the time in production fabrication shops. Basically
any three dimensional joints can be worked out on paper and then transferred to your steel.
RHS joints are fairly simple,its when for example you need to join an angled pipe to a cone that the drawing becomes more complicated.
Cheers
Al
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interestedparty
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| posted on 24/11/02 at 09:30 PM |
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quote:
Originally posted by Wadders
Quite right Chris,what your describing is a
facet of technical drawing called"developement" or in simple terms "templating". Its used all the time in production fabrication shops. Basically
any three dimensional joints can be worked out on paper and then transferred to your steel.
RHS joints are fairly simple,its when for example you need to join an angled pipe to a cone that the drawing becomes more complicated.
Unfortunately my work doesn't already exist as a drawing. I drew up the basic chassis plan but the rest is being made to fit the components which are
already located in the correct positions.
I did think of measuring the actual distances between the two plates on all four corners of the footprint the RHS would make but the angles make that
very difficult.
John
As some day it may happen that a victim must be found,
I've got a little list-- I've got a little list
Of society offenders who might well be underground,
And who never would be missed-- who never would be missed!
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Wadders
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| posted on 24/11/02 at 10:15 PM |
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Unfortunately my work doesn't already exist as a drawing. I drew up the basic chassis plan but the rest is being made to fit the components which are
already located in the correct positions.
I did think of measuring the actual distances between the two plates on all four corners of the footprint the RHS would make but the angles make that
very difficult.
John
Yup this makes things more difficult,and a certain amount of trial and error will be inevitable,but i reckon chris is still on the right track. How
about taking a length of RHS which is a good few inches shorter than the final length required,make up some card sleeves to slip over either end,tape
them on and then offer up to the chassis,mark them up as best you think and then cut with scissors,if they are a bit out adjust until correct,once
you are satisfied with the angles,slide one of the sleeves until the right length is achieved.
Kin ell this sounds like something from a Blue Peter annual,if you end up with a model of the Tahj mahal don't blame me!
Afterthought what about using some 1" square lengths of timber to mock up the tubes first,then wrap card round these and transfer to steel?
Hope this helps
Al.
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Metal Hippy™
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| posted on 24/11/02 at 11:49 PM |
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I personally would go back to your original method and simply swap the angle grinder for a good hand file.
Take it nice and slow and keep offering up to the right position and you won't be far off.
It might take longer than you'd want but it might prevent a lot of fart arsing around with other ideas that will add up to just as much in time
spent...
President of the Non-conformist Locost Builders Club. E-mail for details...
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Alan B
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| posted on 25/11/02 at 03:28 AM |
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If you were using round tube (I know you aren't, but bear with me) there is a tool available similar to what Wadders describes. It is basically two
sets of profiles gauges (you know, the ones with all the pins) that are circular instead of straight.
So with square tube you could do something similar, but instead of the pins 1 folded piece of card or thin sheet metal (with a pointed end) on each
corner held on say with a couple of rubber bands.
You could then gauge the joint in just 4 places each end (which is all you need)
Maybe I need to work on a sketch...
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Rorty
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| posted on 25/11/02 at 04:51 AM |
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I don't use RHS very often, but there's a simple way of measuring the compound angles and the overall length, all at once.
I'm not building a locost or similar, so bear with me.
I recall you're using 1" RHS, or are you actually using 25mm? Anyway, I'll describe the process in metric, and you can change it to suit if
necessary.
Find a piece of 30 x 30 x 2.5mm, say 300mm long. Drill a 12mm hole in each end. Thread a 10mm bolt into a 10mm nut so around 5mm is protruding. Stick
the end of the bolt into one of the holes in the RHS, and weld the nut onto the RHS. Repeat at the other hole. You could also weld a washer on it's
edge to each bolt head, but either way, you basically have 2 thumb screws now.
Cut 2 pieces of your 1"/25mm RHS, and slide into the 30 x30. Set the end of one of the 25mm pieces up against the spot where you intend to mark the
compound cut, and slide the other piece of 25mm RHS out, to touch the other joint area. A couple of welder's magnets would be useful for holding the
ends (if you aren't married). Tighten the thumb screws.
Lay a steel ruler or short bit of 50mm wide flat bar, up against each of the faces of the joints, one face at a time, and scribe the ends of the 2
pieces of 25 x 25 RHS with a Stanley knife or simillar. When all 8 faces have been scribed, scribe the ends of the 25 x 25 that go into the 30 x 30,
using the edge of the 30 x 30 as a guide.
Gently remove the whole assembly to the vice, and measure along from the ends of the RHS, to one of the angled, scribed lines. Note down this
measurement (for the sake of this illustration, let's say it's 42.5mm).
Undo the thumb screw, and slide out the 25 x 25 RHS, and scribe another line 42.5mm away from the one at the edge of the 30 x 30, making sure it's
AWAY from the end with the angled scribe marks.
Repeat this with the other end of the aparatus, and then re-insert the 2 bits of rhs into the bit of 30 x 30, and tighten the thumb screws with the
NEW marks lined up at the ends of the 30 x 30. Smart people will have worked out you can do both measurements at once with one of the telescoping
ends.
In theory, if you now cut along all 8 lines, you'll have a perfectly fitting aparatus.
The next stage is to transfer these marks onto a single length of 25 x 25 RHS. With a felt tip, mark one face of the aparatus with a big "X", and
put a simillar mark on a face of the new length of RHS. These reference marks will ensure you don't lose your place, and mix the faces up.
Working on one end at a time, using a carpenter's bevel, copy the angle of the scribe marks onto the new tube, cut the ends, and you now have a
perfect fitting tube with gap-free joints.
If you ever have to do this with round tube, draw a mark on each tube where they meet the weld seam of the telescoping tube. That way, you can measure
the rotation of the joints!
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
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mooselogic
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| posted on 28/11/02 at 05:14 PM |
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mooselogic
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| posted on 28/11/02 at 05:26 PM |
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I found that cutting the rhs to the correct length first, then using 1inch squares of card with the correct angle cut down one side offered up to the
ends and held in place with some masking tape. (using a piece of card for each side of rhs and just a pen mark for right angled cuts) i then got out
the trusty angle grinder and correct flap disc and ground down to the card edge... job done, everythings fitted together perfectly and as of yet none
of my angles have been wrong.
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interestedparty
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| posted on 28/11/02 at 06:57 PM |
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Well Done Lads!
There have been some good ideas, and very helpful, although a couple of them I must confess to not following in their entirety
The idea that I have already started experimenting with, and getting good results so far, is Alan B's. That's not surprising, Alan being something
of a father figure to us all, even the ones who, like me, are older than him.
I bought some brass angle strip (90degree) from B&Q and have cut 8 pointed pieces, and secured them to each end of a too-short piece of RHS with a
hose clip done up so it's just nipping them. I hold the RHS in position and slide the brass pieces up til they touch, get one end right, do up the
clip and then concentrate on the other. Works very well, thanks Alan and all the others who contributed ideas
John
As some day it may happen that a victim must be found,
I've got a little list-- I've got a little list
Of society offenders who might well be underground,
And who never would be missed-- who never would be missed!
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