Lelit PL041 "copper tube"

Need help with equipment usage or want to share your latest discovery?
Shuka
Posts: 38
Joined: 8 years ago

#1: Post by Shuka »

Hi -
I have a Electrolux Rex (which I think is merely a repackaged LeLit), in which the threads of the "copper tube" that extends down the boiler and feeds the grouphead have become striped (not by me!). I see that 1st-line has a replacement, which looks like it really is copper. However, I'm convinced that the tube in my machine is actually brass (which has about 1/4 the thermal conductivity of copper). I have seen some posts about copper tubes in the boiler bursting, so perhaps this was a bit of an upgrade? The question is, would it be wiser to replace with brass, for strength, or with copper? Is there a worry about galling of brass on brass (i.e. the tube on the brass fitting and brass boiler)?
Thanks for any guidance.
Good morning, Sunshine!

User avatar
bluesman
Posts: 1594
Joined: 10 years ago

#2: Post by bluesman »

Shuka wrote:Is there a worry about galling of brass on brass?
Brass on brass is generally fine, in my experience and from the reading I've done. But if you're talking about this tube -



I'd use the copper piece and not worry about it. I don't know what threads are on it, but it's easy enough to figure that out or call 1st Line and ask. Then you can get a piece of brass tubing the right size and buy a die to cut the threads yourself, if you're really concerned. But for $8, you can buy a spare while they're in stock and replace the one you get now in X years if it gives you peace of mind.

Shuka (original poster)
Posts: 38
Joined: 8 years ago

#3: Post by Shuka (original poster) »

Thanks for the advice. I've already ordered a die - the tube is 6mm with a 0.75 mm thread. I happen to have some 1/4" copper tube, so I'll just turn the ends down to 6mm and thread them, now that you've put my mind at ease.
Cheers!
Good morning, Sunshine!

User avatar
bluesman
Posts: 1594
Joined: 10 years ago

#4: Post by bluesman replying to Shuka »

I think that's a bad idea. Machining most copper tubing is not as easy as doing mild steel - among other problems, it's much harder to maintain a good surface finish. If you leave irregularities or other finish flaws, they'll serve as stress risers from which cracks will form and propogate because of thermal expansion and contraction. You'll also embrittle the copper both from mechanical working and from the heat generated by tooling it. Personally, I wouldn't machine copper tubing because of this (especially to make a $7 part). If you're going to do it anyway, be sure that the reduced tubing still has a wall thickness at least equal to that of the original piece after turning, and that the surface finish is as smooth.

FWIW, here are some quotes from others about this:
  • [C]opper can be a royal pain to deal with. We used to run a lot of 1 1/4" round bar in the CNC lathe at work. Problem with copper is that it is SOOO malleable. It flows nearly as much as it cuts. You could make a threading pass and sometimes it would actually INCREASE the outer diameter, as the metal flowed around the tool. It also loves to grab drill bits and wring them off. We ended up using stub length carbide tipped drills to avoid welding and wringing. On cutoff, the entrance to the cutoff sounded almost like the machine was wrecking as the copper balled up and spit out of the cut. Real nerve wracking the first few times you ran the machine.
  • I hate doing copper way more than stainless. I made a bunch of buss bars out of 14 gauge sheet and it was not too bad, but I had to make a bunch of terminal bars out of 1.25" x .75" inch high purity bar and it was like cutting very tough bubble gum. I had best luck using a corn cobb style rougher turning fairly slow and then doing a light and fast finish pass with HSS. The biggest problem is that if your feeds and speeds are off, it will start to hammer in the cut and work loose in your fixture. For coolant I ran Liquid Ice at about 12%
  • I have machined copper on my lathe and milling machine and find it more difficult to machine than brass or other metals. I use high speed tool steel cutting bits/end mills. The cutting bit tends to "grab" in the copper when machining a groove in the face of a copper plate on the lathe. I have changed my grind angles on the cutting bit but it doesn't seem to help.

Shuka (original poster)
Posts: 38
Joined: 8 years ago

#5: Post by Shuka (original poster) »

Hi Bluesman -
It's interesting, the things that stick in our craws. I don't know why, but I don't want to buy that tube! I guess I want to see the machine I'm restoring work at any level before worrying about a quality fix. This said, I've always enjoyed working with brass... so I'll look for a brass tube instead. Thanks for the pointers.

(P.S. - I did work on turning down the copper today, before I saw your post. It was annoying, in part because the copper was so weak, and in part because the tube I have was already somewhat bent and crushed. Pretty stuff, though.)
Good morning, Sunshine!