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

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 @

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.

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

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

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

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?

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a cruise missile?

snipped

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.

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

--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..

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.

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a cruise missile?

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

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

If you want a "sneak" preview, check out

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

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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

Where are you going to test it? Geoff

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 :-)

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Lee Valley

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