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  #1  
Old Wed 19 January 2011, 19:58
Red_boards
Just call me: Red #91
 
Melbourne
Australia
Tolerance in length of y-beams

The drawings give the dimension of the y-box section tubes as y+500mm.
In my case this is 1240+500 = 1740. My "generous" supplier cut the tubes 1741mm. I'm concerned that I won't be able to trim the 10mm off accurately and leave a square edge. Can I work with the extra length by setting the rails out further 5mm each side or is this going to cause all sorts of problems with flex and/or with setting up the vee bearings and having the motors mesh with the rack?

Of course the most correct answer is to have the beams recut to size..
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  #2  
Old Wed 19 January 2011, 20:04
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Red,
Looks like your only out 1mm not 10mm? I think you should be able to accommodate 1mm.
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  #3  
Old Wed 19 January 2011, 20:26
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
I would be more concerned about the squareness than the 1mm extra length.

10mm needs a recut.
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  #4  
Old Wed 19 January 2011, 21:39
Red_boards
Just call me: Red #91
 
Melbourne
Australia
Thanks for the quick responses.
Yes they are 10mm too long, which means the length is 1750mm (1749 actually, as I recall).
OK, I'll find a cold cut saw that will give a good result. I have some plates to buy, so I think they'll also cut these beams (both at the same time) for a few $

You're right, of course. Once you start playing the 5mm extra game, you have to play the 5mm less game somewhere else and it's bound to end in tears when there aren't any more 5mms to spare.
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  #5  
Old Wed 19 January 2011, 22:14
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
They would be easy to cut with those thin grinding disks. Scribe lines right around, clamp/tackweld scrap flat bar on the lines, grind freehand against the scrap. (test this by taking a sample 5mm off first)
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  #6  
Old Fri 21 January 2011, 08:03
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
...I second the "by hand", quick and easy with a guide strip.
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  #7  
Old Sat 22 January 2011, 22:58
KenC
Just call me: Ken
 
Klang
Malaysia
for 10mm you can go the luxurious way of a cold cut saw, plasma cutter, oxy-cutter...etc
OR you can hack saw the excess by hand & file it smooth. this is the green way as well.
Nowadays, a grinder with a thin cutting disc is the way to go.
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  #8  
Old Tue 25 January 2011, 20:21
Red_boards
Just call me: Red #91
 
Melbourne
Australia
Thanks for the encouragement. I put a thin disk in place, clamped the beams together and worked my way around. Results were not exact (i.e. the beginning and end did not match up completely, but with a bit of grinding they came out the right length and pretty square.
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  #9  
Old Wed 26 January 2011, 01:58
KenC
Just call me: Ken
 
Klang
Malaysia
good job!
It is more important to ensure both tubes are sqaure & equalength to each other. Dimension is secondary.
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  #10  
Old Wed 26 January 2011, 04:52
Surfcnc
Just call me: Ross #74
 
Queensland
Australia
Gidday Red

Australia Day Mechmate construction - I just went surfing , haha

I see you have clamped your bar stock as a cutting quide. As a rule always use two clamps, as a central point will occasionally pivot.
This rule is applicable to ANY guide you might set up including ripping using a power saw, jigsaw, the lot.
The work flow is...
set one edge, set the other edge then check the first then back to the second.

Secondly another guide to ensure the cut is vertical is recommended until you reach guru status with the grinder.

I pretty much can't get my cuts perfect by hand or using a friction drop saw.
What I now do is get it close and use a faceplate sander and a 90degree guide to that face to sand back the cut to perfectly square.
Works really well.

Or you can do none of this and get a Carbide saw like Tony Has !!!

Regards
Ross
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  #11  
Old Wed 26 January 2011, 16:57
Red_boards
Just call me: Red #91
 
Melbourne
Australia
Thanks for the tips, Ken and Ross
I ended up using vice-grips instead of the clamp. They held tighter.
You're right on the bar shifting with a single hold down point (how do I know?).
If I'd have been smart, I would have cut my rails to length and then used the cut-offs clamped either side of the beams. That way the clamp would not have got in the way like the one above and the vice grip (which now has some cuts that neatly match the thickness of the cutting disk). The angles would have made a better vertical guide.

I was lucky on the verticalness because the steel is thin. But I know what you mean. I've just made stopper blocks. Darn hard to get those little buggers flat on both sides (took me back to engineering classes at Iscor in Newcastle where I was give a lump of steel and a file, a few hours and told to make a flat hammer face)!

It just occurred to me that I could have sanded the stoppers using a stiff sanding disk in the drill press. Won't work for the beams, though. They are too long

I searched Google for faceplate sander and got confusing results.
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