perfect joint fitting. is it bad?

[shane7207]

i recently asked the question on which is better? a hole saw style tubing notcher or a punch type notcher that lowbuck tools sells. i got great responses but still have one question on the subject. williams lowbuck claims that you can have too tight of a fit when using a hole saw style notcher.is this possible? they say that when fitting tubing it should be "v'd out" to get a proper fit. what are your thoughts on this?
thanks for the input.

[hankj]

Shane7207,

I'm pretty much of a rookie welder, so I've asked a LOT of questions to a LOT of people. One of the guys I met recently builds engine mounts for aircraft, and we talked about welding thin-wall tubing. He welds a lot of 4130 tube, and his advice was to have as tight a fit as you can get. He also advised that, as you get into thicker tube, you need to bevel the edges, but the fit should still be tight.

Hope this helps.

Hankj

[H80N]

Shane
i concur HANKJ's answer is right on the money as far as my experience goes... used to do quite a bit of race car fab (sportycar)using thinwall 4130.. and was taught to keep the joints as tight as possible... so as to produce an almost fusion weld at the junction adding only sparing amounts of rod as needed... this was TIG welding... cannot make a reccomendation for mig...
hope this helps
Heiti

[Blondie_486]

Shane,

You could get about as many answers to that question as there are welders. For thinwall especially 4130 I keep them as tight as possible but for mig or stick welding thicker wall tubing I like a slight .025 or so gap and beveled edges. For pipe I like to leave about 1/32 for smaller diameter pipe to 1/16 gap on larger diameter pipe again with beveled edges and for the really heavy stuff 1/2 and greater wall thickness I bevel down to a 1/8 nose and leave a 3/32 welding rod gap and run my root pass hot. I think it all depends too on how everyone was taught to weld tubing and pipe joints some of us learned from the old time rod burners where everything had to have a gap in order to acheive penetration. I learned to weld pipe and notched joints in a shop where it was required everything had a gap so I pretty much got used to welding my root pass with a gap in it.

But for what I think you're trying to do myself I keep them pretty tight especially if you're tig welding 4130, .095 mild steel is a little more forgiving than 4130 when it comes to gaps. I would still go for the hole saw type notcher and if you need a little bit of a gap just cut the piece a snitch short so you can leave a gap. You will be so much happier with a hole saw type notcher, I've used both and the only one I want to have is the hole saw type but I use a broach instead of the hole saw but the hole saw works just fine too.

I hope this helps
Blondie_486

[H80N]

Shane
I prefer the hole saw variety... with a couple of caveats... run the saw at as low an rpm as you can get in a drill press and keep the blade wet with oil or wd40 type lube... to carry off the heat otherwise you will use a lot more blades than you need to... had a neat setup that I sold... am piling parts to build another... basicly a drillpress with a jackshaft w/pulley between motor and drillpress to reduce the speed by half... that gives me approx 150rpm at slowest setting... one of the hole saw type notchers mounted to the table.. with a pan between it and the table(w/drain in one corner) and a small parts washer w/pump to spray coolant (the little one from harbor freight works well) using water and soluable oil... took a pulley approx 16 inch attached to the drillpress down shaft (where the three spokes usually are) and wrapped some nylon cord around it with a sash weight at the end...
kind of a convoluted explanation.. but the setup will fishmouth tubing without constant attention ... blades stay sharp so the cuts are about as nice as you can get with a GOOD quality holesaw blade..
the weight keeps light even pressure on the saw and the low rpm plus the coolant preserve the blade...
hope this makes sense... expect to build this after the snow is gone as most of the parts are buried outside the shop in the white stuff..
When I finally get around to doing it will take some digital pics to better illustrate...if anyone is interested...
Thanks
Heiti

[ASKANDY]

Shane,
everthing you read here was great. Like Heiti said, on race car stuff, tight is right. I assume most of the stuff you are doing is light fab and if 4130 is going to be a part of your work, then tight is a must with a close eye on not overheating.

A-

[shane7207]

thanks for all the responses. i thought tighter was better but i wanted some professional opinions. i like the lowbuck notcher for its quickness but it doesnt produce as good of a fit as the holesaw kind. thanks again.