couple of questions regarding tube thickness, brazing and milling

[arregui]

Hi everyone!

i have two simple questions and i put them together as i think they are quite simple and didnt want to make two posts (hope thats ok).

Both questions are related to working with thin tubes

1-One of the guys who taught me some things of this craft told me that when fillet brazing, seat tube has to had a sleeve in the upper part where it is brazed to the top tube. The reason he gave me is that most of seat tubes are too thin in the portion were the seat post goes so i should make it a little stronger by adding that sleeve. This makes sense.

1a-how thick has to be the wall of the seat tube, in the upper part, to be safe?
2a-How do the TIG guys do this?

I suppose that depending on the type of tubes (alloy or profile) and the weight of the rider it has to vary, but i just want to have a genereal idea of whats your experience with this.


2-This one goes for the people who use a milling machine to make miters.
With a soft steel cheap tube doing a miter with a hole saw it´s easy, gently use the lever, don't push too hard and miter comes perfect.
With thinner tubes and more crispy alloys isnt that easy (in my experience).
Providing that we have a tight grip of the tube:
What do you guys recommend to make this task?

Bigger miterings, as the one for the BB, with Columbus Zona could be a nightmare...

any input will be greatly appreciated!

greetings from Madrid,

Andrés

[Amaro Bikes]

Hola, Andrés.

For your first question, main reason is that due to heat distortion, once you ream the seat tube ther're lot of chances you'll make this tube thickness even thiner, and as this being a quite "suffering" area (three tubes end on the seat tube, lot of heat affected area), future failures due to fatigue are quite high on the probabilities. Most of this "problem" happens as once you go out of the lugged construction, if you use any of the ST wich originally designed for lugged frames, you're actually missing quite a big thickness/reinforcement from the lug.

Solutions are many:
-Use some of the new external butted tubes specially made for this situations. There're many different diameter and lengths, and usually go as thick as 1,2mm so you should be ok. This is usable both for brazing or TIG welding.
-Use some of the special seat collar/sleeves as ones made by paragon intended to work as top seat tube, so you just braze or weld this part on top of seat tube and this would be the area for tt and ss to end. This sleeve is also available on different diameters and are quite thick. One example:

-If brazing, you can use something similar to Steve's "trademark", wich are seat tube reinforcement sleeves, wich would be brazed around the top area of seat tube, being then quite a thick section. Something similar to having a lug, but without the tt/ss holes. This is one example:

-Finally, you can also reinforce the inner part of the tube using a bonded aluminium sleeve or brazing a steel sleeve. In both cases just choose the sleeve up to your ID seat tube diameter (-0,4mm for bonding) and your intended seatpost diameter. Most of the new seat tube steel tubes are actually supplied with such an aluminum shim for bonding, so it's quite straight forward.


For the second question, sorry... I just do it all by hand/file so not much experience with mandrels or hole saws.

Cheers.

[bencooper]

For 2, try finding some fine-pitch hole saws - I use 10tpi ones. Contrary to the usual advice, I run a high RPM with very gentle feed and cutting fluid, and I rarely have a problem with snagging.

[John Winston]

The more rigid your setup up, the better. You shouldn't have any problems mitering the good stuff with hole saws. You just need a rigid setup, low speed and feed, all day long.

[arregui]

Aimar:

So i see two possibilities:

a-Weakening of the joint because upper part is too thin, no heat distortion involved (that point will be weak because we chose wrong the tube).
b-Combination of heat distortion followed by reaming that leads to weakening (the reaming weakens that point).

You bet for the b option?
I has the impression it was more a...

I avoid heat distortion by using heat sinks and heat control (low temperature). As someone here pointed before, at least with fillet brazing, if you manage heat no distortion takes place. Perhaps thats different with TIG???.
So following what you say if i can avoid any distortion i could use 0.8 mm thin tube???

My question was aimed to numbers thought. Never used Columbus Zona seat tube external butted 0.8-0.6-1.2 but i will take from your answer that iam safe working with this without sleeve for fillet brazing.

B. Cooper - 3Wfab

Rigid set up = nice milling machine, short hole saw arbor, tight clamping of tube. Anything missing?

3WFab are you using something like: low speed (for a 40 mm hole saw 220 rpm) works with 4-6 tip?

B.Cooper 8-12 tpi (fine pitch) at what speed would you use for a 40 mm hole saw?


Regarding feeding, manual or auto (what speed?)
Until i got this clear i will stick with hand mitering. I have nightmares of hole saws with huge teeth getting caught in big diameter thin tubes...


Thank you all!

[bencooper]

B.Cooper 8-12 tpi (fine pitch) at what speed would you use for a 40 mm hole saw?

As fast as my DeWalt goes ;-) 1200rpm or so I think.

Manual feed, definitely - I find that I don't need to push much at all, it pretty much pulls itself into the work. I was worried about snagging too, but best thing to do is have a go with some old tubes and see what happens.

[John Winston]

setup: whatever mill you have. the least amount of tubing 'sticking out' from where it is clamped. as short of an arbor that will get the job done. your mill quill retracted (for starters)
I run my spindle speed around 165 rpm. manual feed is fine (though boring). If you've auto feed, that will free you up from standing at the mill for a few minutes.
It exciting when your feed is too fast or your setup isn't rigid. Usually results in a broken tooth or two on your saw, and a chewed up tube. Either way, if you were sleeping, it'll wake you up.
Experiment. You'll find there isn't any issue mitering on the mill.

[Eric Estlund]

For tubes, it's a and b.

[Amaro Bikes]

Hola, Andrés.

It's not just a or b, but as Eric said, both parts take place. 0,8mm thickness tube without the previous lug "reinforcement" makes a thin tube (hainv in mind you're actually surrounding it by three tubes (tt+2ss) with their HAZs. Also, the thinner the tube, the more easily heat distortion to happen
The use of heatsinks is helpful with TIG (although not necessary if you manage good travel speed), but not so sure about it when brazing as they'll take heat needed on the tubes to make the silver/brass flowing.
When Tig welding you'll also have to keep in mind the welding puddle "geometry" avoiding any "peak" or "discontinuity" where tensions will accumulate and create a possible failure on fatigue after time.

If you ask for my personal opinion, I would go with a minimun 1mm thickness on the area, with also a bonded alu shim (I do usually go with 31,7 seat tubes and 27,2 seatpost, so enough space for the shim and much more confidence on the long time realiability).

Cheers

[steve garro]

As fast as my DeWalt goes ;-) 1200rpm or so I think.

Manual feed, definitely - I find that I don't need to push much at all, it pretty much pulls itself into the work. I was worried about snagging too, but best thing to do is have a go with some old tubes and see what happens.

This is in jest, right?
- Garro.

[bencooper]

This is in jest, right?
- Garro.

No. I know the rules about cutting speeds and this goes completely contrary to them, but it works very well with this setup.

[ToddFarr]

This might help some find a starting point for holesaw RPMS. Found it flipping through my black book yesterday at work.

[bencooper]

Yes, though it's worth pointing out that those speeds are assuming the hole saw is cutting into a flat surface so quite a few teeth are in contact with the material. Mitring a tube, you're effectively cutting edge-on, and even with a 10tpi hole saw you only have one tooth in momentary contact with the material at any one time.

[Andrew R Stewart]

I've read the many posts over the years about cutting speeds, hole saws, tooth counts and such. I agree that rigid set ups are first and formost important. But I found with both my loose Atlas 6" lathe and the Joint Jigger I had the faster cutting speeds worked better. Truing up or grinding the hole saw's outside is a good idea. Always wanted to try Andy S's cutters but at the rate I build a hack saw, grinder and file is almost as quick and much easier to set up. Andy.

[arregui]

Thank you very guys for sharing.
I think i got they idea on the seat cluster joint vs. thin walls.

on the hole saw issue not that clear thought. I guess this is the point to try and error.
I tried high speeds before and with some tubes the thing get really hot and teeth cant go through.
the right conditions to make a nice cut seems to depend much on the type of alloy.

ill try low and high speeds with 4 tpi and 10. ill try grinding (Andy you mean like sharpening, right????) the outside of the hole saw also.

again thanks, i i can say something new out of my cuttings ill keep you posted.

Andrés

[Andrew R Stewart]

Andres- You can grind a hole saw in a few ways to improve the cutting. The roundness can be touched up by grinding down the high spots (like where the seam is). I've seen people attach a die grinder to their lathe with the hols saw in the chuck to do this. I've also seen people modify the tooth shape. Lowering their height and lessening the back rake a bit. Andy.

[ToddFarr]

I don't have much experience notching tubes, but the same thing happens when milling if you are running your mills or drills to fast and not giving enough pressure to bite, your coolant will evaporate instantly, you will heat treat the surface of the part and your tool is basically done. If you are gonna run higher speeds make sure to keep that pressure so the tool is always biting and removing chips otherwise its spinning and creating heat. Heat is always the enemy, so take the necessary steps to keep it under control.

-Todd.

[bencooper]

Hole sawing a tube is much more like hacksawing than milling, I find that a good way to think about it.

[18bikes]

I'd agree with Ben that it's more like hacksawing but I'd disagree about his speed. We use a Harrison mill, here is it's speed chart


Harrison Horizontal Milling machine by 18bikes, on Flickr

Most of the time I have it set on 234rpm, but I find the smaller holesaws need to go faster, usually the 4XXrpm option but sometimes I go up to 613rpm. It depends what the material is. I find that the wall thickness makes more of a difference than what the tube is made from; I can run a thick will tube faster and really plough my way through it. The main reason I run slower (than Ben) is that I have to hand feed the tube into the cutter and it can grab when run faster. I'm goig to try the holesaws Ben uses when I next need to buy some so I may find I can run them faster but I'd still be very wary of running them at 1200rpm (although for me it would have to be 958 or 1500). I used to run flood coolant when I used the lathe but never got round to switching it over to the mill and it's never hurt. A few drops of a normal cutting fluid and I'm fine

Matt

[bencooper]

I'm just guessing at 1200, by the way - I normally use the top speed on my drill, but not always at full throttle. I find I can feel if it's sawing nicely through or not, and vary speed and pressure as I go.

I guess what this shows is there's no right answer ;-)