ira wrote:Staying in line with old machine names, I keep coming up with Maribel. Since the current target audience is probably this board, it likely doesn't matter what you call it at first.

Commonly when you want to slip tubing over a shaft, you use lubricant, air or both. Use a water based lubricant that is not harmful to the metal and it will dry in a bit and the tubing will likely never move. Or plug the shaft and put an air nozzle with a plate to seal against the end of the tube and it will likely go right one once you get the hang of it.Get enough air going through there and the tubing slides on a film of air.

Ira

Probably you're right, not much difference what it's called. Still, I'd like you guys (and myself) to be able to tell people who see it the name of it without getting too much of a funny look!

Thanks for the idea, I had thought of hooking it up to a hose and seeing what happens, my idea straight after that is it will probably be something hilarious. Air seems a bit like a safer idea if I had a compressor, I'm sure I can find one. Still I think I need to move up a size or so in tubing, what I got I think will be just too small. I wanted it to be snug so I didn't want to get a size too large, but I think with the type of material it seems super sticky anyway.

Water or air would work though with water you'd want constant flow, not a normal hose. Watch any motorcycle mechanic put grips on or off and thats what they do unless the just cut the old ones off. It just makes them float on the handlebar so it's easy to get them on and positioned.

Ira

bluesman wrote:Hmmmm - I have both a lathe with threading dial / gearset and a TIG welder. It would take me no more than 5 minutes to heliarc that tube to the plate. Cutting two threads that size would take far longer, even with CNC, because you have two setup and machining operations each of which will require multiple passes. A heliarc bead would require only one pass alternating from side to side to avoid warping. So I don't understand why welding would cost you more.

So looks like the threading in just tools is going to cost too much...going to have to revisit welding the main pipe in. The 1/8" NPT thread for the gauge could be done with a normal reamer and tap set I'm told...but thinking as long as im getting the pipe welded, maybe I should have a 1/8"npt fitting welded in as well? Or would a part that small not weld on stainless?

ira wrote:Water or air would work though with water you'd want constant flow, not a normal hose. Watch any motorcycle mechanic put grips on or off and thats what they do unless the just cut the old ones off. It just makes them float on the handlebar so it's easy to get them on and positioned.

Ira

Thanks Ira, I'm getting some larger tubing in, as well as some foam tubing, going to see what works out best. Will post up some pictures once I get parts in. I also had the idea to try out cork grips for bicycles, but some reviews of the cheaper cork crumbling kind of put me off.

Other than that, shots are going well, I've been using the machine mostly exclusively...I bet Miss Strega is wondering what's up. She just gets to steam milk occasionally these days. Though I have pulled an occasional shot when she's heated up for steaming already.

Maybe I'm wrong, but I think welding has to many potential problems. I still think press fit or glue is the right answer. There is no pressure trying to move the tube in the head. Welding will cause the tube to warp and you'll get a higher failure rate from leaks and faster o-ring wearing. 032 wall wall stainless tube pressed in a machined base will be easy and relatively inexpensive. You can always flare the bottom with a big punch if you're worried about pullout. You'll only need to flare it about 5 to 10 thousandths to keep it from pulling out.

Ira

The tube itself wouldn't be welded, it would need to be a seamless pipe, but welded just at the very bottom to the plate on the inside. My understanding in general is that welded fittings in the piping world are much less likely to leak, especially over time. This probably has more to do with corrosion which shouldn't be much of an issue with this machine in stainless. As bluesman mentioned, he would weld on alternating sides to avoid warping.

I see 0.035" wall stainless tubing rated at 1875 psi pressure....why would schedule 40 stainless pipe be rated only at 160 psi? Although it's probably fine beyond that pressure some for bursts. The pressure rating would be more for continuous pressure. But still seems like something weird is going on there. Both are 304 stainless.

Still for some reason, even with press fitting flaring the bottom...it seems like it wouldn't hold pressure, at least over time. I'm probably wrong here, but just feels uncomfortable.

[edit] I didn't realize until more research that you're probably thinking that an o-ring or something would be added between the wall where press-fitting. This video on their page gave me a bit more idea of the process:

http://www.victaulic.com/en/businesses- ... teel-pipe/

Although they are selling the proprietary fittings and clamp, I could use some idea like that. It does seem cheaper than another method, but I'd still like the mechanical joining to be tight enough. If the press-fit was fairly tight, or if like you say I could flare the end. I'm thinking the main thing to design would be to make sure it could handle the downward force of pressing on it. According to the pressure I was recording on my bathroom scale, it's not a ton of downward force, but would want to make sure the pipe can't slide down.

Thanks for the idea!

Looking more into press fitting, some have also recommended to bake the plate in the oven, and freeze the tube. If dimensions are right, it should drop into place (similar idea as someone mentioned about fitting a PVC sleeve onto the outside of the pipe). Although you only really have one shot at it...

EspressoForge wrote: According to the pressure I was recording on my bathroom scale, it's not a ton of downward force, but would want to make sure the pipe can't slide down.!

There is no downward pressure on the tube.

Ira

In theory, that should be the case, but between friction of degrading o-rings, pressure as you complete a stroke from the handle, and pressure from travel, I wouldn't want to count on no pressure bring exerted at all. Also, when locking in the basket, some rotational force is on the pipe as well.

But as mentioned, it doesn't need to handle a lot of force, so I think pressure fit is ok, or even tight fit and tapped into place with a hammer. But if an o-ring is needed for a good pressure seal, I would like it to be user replaceable.

Tri-Clamp fittings as used in beer brewing lines seem like a nice idea. Extension tubes can be had, and supposedly they come in 3/4" diameter, unfortunately all I can find available are expensive. Most common in beer is 1"-1.5" for homebrew, or bigger for larger setups, so 3/4" isn't as readily available. I'm also not sure if an extension would be welded anyway, or seamless.

But it got me thinking to machine a piece on top plate that could accept some kind of removable fitting, mostly thinking that if a rubber seal was needed for tubing anyway, might as well make it replaceable. I could also possibly machine a compression fitting into the top, so you could ideally slide in a piece of tubing, then tighten the fitting down with a wrench. Again, will have to see what is a bigger deal in machining.

The original prototype machinist I used was going to be too expensive for this project. He's concerned about working with stainless and added a ton of labor for machine time (watching the CNC). I don't blame him, it seems like he would rather work with another material...but I feel like stainless is where the project needs to go. I have another source for a machine shop, will be getting more details with them since it looks like they have a bit larger CNC setup and sounded like they'd be able to do a small production run at an affordable price. Hopefully that will be the case and we can get the beta units out for a reduced price from my planned final price.

Other parts started coming in as well, new pressure gauge and a stainless funnel. Once I get the grip material and some other o-ring materials, will report back. Tried out a 90A nitrile o-ring...very hard, ended up breaking it just getting it on. AFLAS is coming in at 80A and 70A silicone seemed a bit too soft. So we'll see!

You could do both, press fit AND tack weld it in a couple of spots.
Also, you probably want to do yourself the favor of finding a place with enough experience in machining stainless, that really takes some experience and sometimes slightly different lathe bits or settings....a former relative of me has an engineering and fabrication shop and slowly specialized in stainless and other exotic steel types and gets work from all over the place because other shops just don't hack it or shy away.