Making space-frame chasis -- how to fit-up?

I'm about to make a fairly complex space-frame chasis for a large jet-powered vehicle that will be attempting to set a speed record (details to be released soon:-)

What I want to know is: what's the best way to cut tubing so that you get a good fit-up when joining one piece of tube at an angle to another?

In the past I've just used the chop saw to get the angle right and then ground the concave contour in the end so that it's a neat fit against the other piece of tubing -- but this is awfully laborious -- surely there's a simpler way?

Given that there are only a limited number of angles involved but lots of bits to cut, I was wondering whether it might be worthwhile building a jig and using a hole-cutting saw to cut the tubing to length/angle. This would automatically produce the correct radius of curve to produce a nice tight fit -- although I expect I'd go through a few saws to complete the project.

How much effort should I be investing in getting a realy close fit between the parts anyway? I'll be TIG welding so I guess the better the fit-up the better the weld but how good is good enough?

Is TIGing the best choice for this type of work -- remembering that I

*don't* want this falling apart at several hundred kilometers an hour :-)

I also have MIG and oxy welding facilities.

-- you can contact me via

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a cruise missile?
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Reply to
Bruce Simpson
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No suggestions (well, on Monster Garage, to do something like this they take the chopped pipe over to a nice fast belt sander and plunk it on the round end, but that only works if the pipe is the same diameter as the guide roller), but it's good to see you're still at work. Any updates to your website lately?

Tim

-- "I've got more trophies than Wayne Gretsky and the Pope combined!" - Homer Simpson Website @

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Reply to
Tim Williams

We build a new frame each year, 1" tube. We use a pair of clamp blocks and a 1" roughing end mill in a Bridgeport mill. Goal is to get all angles +/- 1 degree, length +.000", -.030" Idea is that max gap is .030" on .065" and .083" wall tube. Target gap is .015" to .020" Makes welding with TIG or MIG easy.

We have a Excel based table of offsets so that you can either take the center to center distance or the actual distance and use that to set up the mill exactly right the first time.

Harbor Freight has a drill press rig, works ok but not great.

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Bruce Simps> I'm about to make a fairly complex space-frame chasis for a large

Reply to
RoyJ

It probably isn't worthwhile to build a jig, since you can buy joint jiggers already built. Here's one from Harbor Freight

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Depends on the tube thickness. In general, the gap shouldn't be greater than half the tube wall thickness.

I'd use TIG, with O/A as my second choice. If you have the correct parameters dialed in, MIG would also be acceptable, but it is so easy to get a good looking weak weld with MIG that I'd be hesitant to use it for such a critical welding job.

Gary

Reply to
Gary Coffman

As chance would have it, someone asked a similar question in the sci.engr.joining.welding newsgroup and a number of answers have been forthcoming -- what are the odds eh?

-- you can contact me via

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a cruise missile?
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Reply to
Bruce Simpson

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We MIGed the last frame. Setup was to get really tight fitups, did heavy tack welds then ground them down for minimal stickout. Used some .023 wire, tried all the Mig outfits to see which one did the best (the Century won out over the Miller ??!!!!), spent quite a bit of time dialing in the settings before starting. Had 3 people during welding: 1 welder, 2 helpers to flip the frame. All welds were downhand. Took a couple hours to do about 6 joints. I was pleased with the results. It wasn't a stack of dimes look but it had good penetration.

Reply to
RoyJ

Bruce, given that you are in darkest Tokoroa (think Deliverance :-) your options are a bit limited. Have you still got the drill mill? If so, best way is to use that, make a jig to clamp the pipe at the right angle and take a slow cut with a holesaw or endmill (if it will take it). Come up to Auckland and use my horizontal mill if you want. Geoff

Reply to
geoff m

--Note: the problem with the "joint jigger" style of tube end cutter is that it only works on a floor-model drillpress. If you've got a bench model it just won't fit..

Reply to
steamer

Thansk Geoff, yep I've still got the mill so I'll make up a clamping jig and use the holesaw approach.

You'll have to come down and visit sometime.

I guess I should use a holesaw that fits in a mill-holder rather than one that fits in the drill-chuck though -- considering that there'd probably be significant side-loading produced by having only one side of the saw cutting.

-- you can contact me via

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a cruise missile?
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Reply to
Bruce Simpson

I'd also suggest trying the endmill technique. I've done lots of 1" X .083 stainless ornamental tube for boat rails this way. The advantages are near perfect fit-ups and the ability to make very small adjustments to the joints after trial fit up.

Ned Simmons

Reply to
Ned Simmons

Getting enough speed from the pulsejets to light the ramjet will be interesting :)

Reply to
Ian Stirling

If you want a "sneak" preview, check out

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also check out
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Of course if any prospective sponsors are reading this, just drop me a line :-)

-- you can contact me via

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Reply to
Bruce Simpson

One other comment about holesaws (apart from "buy good ones"). The teeth are really a bit coarse for tubing and they tend to grab if you are not careful. I have never seen "hacksaw teeth" holesaws, but that is what it really needs. Take it really carefully and use lots of cutting oil. You should be able to modify a Blumol arbour to fit a MT3 stub arbour. Be more solid than using the milling chuck. Geoff

Reply to
geoff m

Where are you going to test it? Geoff

Reply to
geoff m

I'll be doing the initial tests on the Tokoroa airfield but it's only

1,100 metres long so I won't be expecting to hit much over 160Kph.

The actual record-attempt may be up at 90-mile beach (although I expect I'd probably have to get some special resource consent and the blessing of the local iwi :-)

-- you can contact me via

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Reply to
Bruce Simpson

Lee Valley

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sells diamond coated hole saws. Never used one, but it wouldn't have the tooth size issue. Supposed to cut glass, ceramic and metal.

Chris

Reply to
Chris

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