juan benech
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| posted on 11/11/04 at 09:39 AM |
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tube cutting problems
Hi Builders
I'm reading the book using a dictionary because my language is spanish, and I just have started welding classes this week, so as you can see, I
am very new.
I've found my first problem when I started cutting some tubes to test my welding.
My plans are to cut my tube lengths using a hacksaw, but I found out that it's not easy to cut square faced ends, and I don't want to
think about angle cutting or even measuring angles.
any suggestion? thanks
Juan
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splitrivet
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| posted on 11/11/04 at 09:47 AM |
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Buy yourself an attachment to turn your large angle grinder into a chop saw.
Its money well spent.
Cheers,
Bob
I used to be a Werewolf but I'm alright nowwoooooooooooooo
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Mix
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| posted on 11/11/04 at 09:50 AM |
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Unless you want to go to the expense of a chop saw or an angle grinder attachment that performs a similar function I would suggest that all you need
to do is practice, you will soon get the hang of hand sawing.
Cut the tube 1 or 2mm oversize and tidy up the cut with a file or angle grinder.
Mick
[Edited on 11/11/04 by Mix]
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David Jenkins
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| posted on 11/11/04 at 09:55 AM |
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You will need a couple of marking-out tools:
- a scribe (a hardened sharp point to make scratches on metal)
- a protractor (click here)
Mark the metal with the scribe and protractor, so that all the angles are correct and the end of the last line meets the start of the first one.
Hacksaw close to this line, then use a file to finish it off. You'll now be exactly right! (or good enough for welding, anyway).
Some people use an angle grinder in a mitre frame, but I found the hacksaw and file method worked perfectly OK.
Hope this helps!
David
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stephen_gusterson
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| posted on 11/11/04 at 10:09 AM |
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make or buy a saw guide block
atb
steve
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Bob C
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| posted on 11/11/04 at 10:10 AM |
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It sounds as if you're just hacking straight through with the hacksaw. Don't.
Mark a scribe line on each face as described above and saw on the waste side if the scribe line on each face separately.
If you just hack straight through tube the saw kerf will wander & you can't stop it. It's also impossible to cut the more acute
angles.
No big deal - doesn't take long. I hacksawed my chassis in about 2 days work - welding took rather longer.
Bob C
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Peteff
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| posted on 11/11/04 at 10:14 AM |
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Draw your angles on all sides of your metal and cut one side at a time till you get better at it. It takes longer but there is less tidying with the
file. You soon get good at filling gaps with the welder if your cuts are not perfect.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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James
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| posted on 11/11/04 at 11:13 AM |
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Get an angle grinder with the really thin ( less than 1mm) blades.
You'll be through each tube in about 10 seconds!
Also, you probably know this from reading the forum, but don't cut all your tubes at once as there are mistakes in the book cutting list.
Goto http://www.mcsorley.net to get an accurate chassis plan.
Also, get in contact with Alez on this site as he lives in Madrid.
Hope that helps,
James
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Mechman99
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| posted on 11/11/04 at 01:43 PM |
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I am at the same stage.
A mitre cutting jig with fine blade and adjustable angle works very well, just needs a touch with a file to de-burr.
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blueshift
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| posted on 11/11/04 at 02:19 PM |
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Try not to leave gaps due to wonky cuts that need to be filled by the welder - it leads to distortion of the chassis. Snug fits are best.
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MikeRJ
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| posted on 11/11/04 at 03:30 PM |
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If I have a compund angle to cut on a square tube, I scribe the line on every side and then hacksaw down one side at a time, turning the tube 90
degrees in the vice after each cut.
The angled grinder jigs are ok for 90 degree cuts, but the one I have is not made very well, the pivot has a lot of slop so I don't use it for
anything that needs good accuracy.
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David Jenkins
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| posted on 11/11/04 at 03:48 PM |
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I cut tubes when I needed them, using a hacksaw and file. I'm fairly good with these tools, and could cut and finish a piece in well under 5
minutes (after marking out).
I know an angle-grinder jig might have done it quicker, but I did most of my work in the late evening and didn't want the noise, burnt metal
smell and the pervasive abrasive dust everywhere (I have a number of machine tools nearby) - my garage is attached to the side of the house, and I
wanted to stay on good terms with my neighbours!
Anyway, I find hacksawing and filing strangely relaxing! 
David
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kb58
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| posted on 11/11/04 at 03:56 PM |
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There is a perception that it's easier to build a square-tube chassis then round tube. Cutting square tubes in a single plane is one thing, but
just wait until you have to cut the tube when it's coming in at an odd angle to meet two other square tubes. Much, much more difficult and a
hacksaw or even bandsaw won't get it done. This is where using round tubes is superior. Carefully pick and choose what type of tubing you want
where. Square tubing is normally used only when paneling needs to be attached. IIRC the locost doesn't have many/any compound off axis
junctions, but just be aware round tubing is easier to deal with in that case.
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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David Jenkins
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| posted on 11/11/04 at 04:26 PM |
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kb58 - sorry, but I disagree with almost all of that!
I had no problem with odd angles in square tube, but had to use that mitre software on my PC to get round tube correctly cut (I hate welding round
tube as well!)
...but that's just my opinion (see sig below)
David
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Mix
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| posted on 11/11/04 at 04:31 PM |
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Sorry, just thick I suppose but I can't see how cutting a compound mitre using round section can be easier than using square section. (Assuming
using only basic hand tools).
Would you enlighten me ?
Cheers Mick
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David Jenkins
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| posted on 11/11/04 at 04:37 PM |
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I guess it's because you don't get the 'angled in 2 planes' problem you get in square (e.g. the uprights on the radiator mount
on the chassis). You're always going to get 'angled in 1 plane' on round! However, I always found getting the angled cuts in the
correct orientation at each end of round tube very difficult - that's MUCH easier in square!
David
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Mix
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| posted on 11/11/04 at 04:46 PM |
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David
I think you've hit the nail on the head there. With round section there is no easily identifyable base reference whereas with square there are
four.
I'll be sticking with square section wherever possible.
Mick
Oh and wasn't KB58 refering to a three tube junction.
[Edited on 11/11/04 by Mix]
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juan benech
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| posted on 11/11/04 at 05:53 PM |
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Thank you guys, lots of good advice , Im sure that I could do the job now.
Pablo
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gazza285
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| posted on 11/11/04 at 07:46 PM |
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quote:
Originally posted by blueshift
Try not to leave gaps due to wonky cuts that need to be filled by the welder - it leads to distortion of the chassis. Snug fits are best.
Leaving a slight gap is actually the prefered method of welding thin wall tubing as the weld then fills the joint (rather than sitting on it), leaving
a stronger weld. It also allows for the weld to be ground down flat without too much strength loss.
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Rorty
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| posted on 12/11/04 at 01:58 AM |
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quote:
Originally posted by gazza285
Leaving a slight gap is actually the prefered method of welding thin wall tubing as the weld then fills the joint (rather than sitting on it), leaving
a stronger weld. It also allows for the weld to be ground down flat without too much strength loss.
I disagree with this. Leaving a gap and filling with weld will cause the chassis to distort an amazing amount. Because there is no parent
metal-to-metal contact, the weld "bridge" cools and shrinks, pulling the parent with it. A tiny amount of shrinkage can end up as quite a
few degrees over the length of a chassis tube.
I have found the best method is to roughly bevel all the ends on the grinder before welding. This has two benefits: it removes any ragged edges and
it provides a "nest" for the weld to penetrate deeply into the joint. The bevel still retains a hard edge for that perfect metal-to-metal
contact.
Ocasionally I will drill a hole through a welded joint and plug-weld the hole up again, just so the cooling weld will pull the part into alignment.
The opposite is also possible by heating the opposite side of a tube to the weld and letting it cool. The metal will always move in the direction of
the heat. It's the principle that old-time sheet metal workers used to stretch and shrink those S-shaped chassis rails.
I also agree with kb58 about working with round tube. I find it infinitely simpler and a lot quicker than working with square tube. Admitedly, I am
now profficient enough to cut the fishmouths accurately by eye almost every time, but even as a beginer, I found it quite easy.
The trick with welding round tube is to mentally divide the entire weld bead into three sections. I start welding, shift my weight onto the back foot
and prepare to finish off the first section. I then quickly shift myself without really letting up with the welder, weld the second section and again,
shift my weight onto the back foot and complete the weld. That always results in a perfect continuous weld.
It's nauseating every time I hear it, but "practice makes perfect".
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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kb58
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| posted on 12/11/04 at 04:40 AM |
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Rorty... that's one heck of an avatar. Was that lifted from a video game or digitized footage of an actual model. Pretty amazing if it's
computer amimated.
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
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cassidym
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| posted on 13/11/04 at 09:25 PM |
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Very informative post. Thanx guys, cleared up a few issues I had myself.
Agree with Rorty re no gaps. Been practicing on 2/1.6/1 mm for the past few months MIG/TIG. Found that any gap tends to distort the piece when fully
welding - even after clamping and tacking. Also found that 1.6 is thin enough so no gap is required. Have'nt tried bevelling yet but will do
so.
Always used soapstone markers then got scribe a few weeks back - much more accurate, better fitup.
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gazza285
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| posted on 13/11/04 at 09:40 PM |
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That's 15 years of pipe welding experience up the spout then.
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Rorty
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| posted on 13/11/04 at 09:40 PM |
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quote:
Originally posted by cassidym
Very informative post. Thanx guys, cleared up a few issues I had myself.
Agree with Rorty re no gaps. Been practicing on 2/1.6/1 mm for the past few months MIG/TIG. Found that any gap tends to distort the piece when fully
welding - even after clamping and tacking. Also found that 1.6 is thin enough so no gap is required. Have'nt tried bevelling yet but will do
so.
Always used soapstone markers then got scribe a few weeks back - much more accurate, better fitup.
I would agree, 1.6mm (1/16" doesn't really require bevelling, but a clean-up with the grinder, or even a wire wheel mounted on the
grinder, will remove all the dross and sharp edges.
Chalk has no place in a workshop except when cutting a six metre length of steel in two. I prefer to use one of the small snap-off blade disposable
craft knives to mark out with.
I also use a carpenters marking gauge to establish the centre line of RHS and flat bar prior to drilling holes etc.
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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cassidym
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| posted on 13/11/04 at 10:18 PM |
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gazza, I do humbly apologize for contradicting you and must admit that I'll never be able to equal your welding skill as a pipe weldor.
But it really do seem to be easier for a newbie weldor like me to maintain correct alignment on thinner materials when there is no gap.
For the past few months I've also been welding sheet metal panels into one of my cars and have done extensive research beforehand. The general
consensus was to maintain a slight gap BUT I've found one article where the guy recommended no gap. Tried both ways and concluded that a slight
gap not only leads to misalignment but also easier to burn thro. No doubt that as my skill improve (hopefully) I'll be able to weld thin
materials with a gap but at this stage it is too much of a batlle.
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