Newly acquired Microcimbali Liberty: had a few restore questions - Page 3

#21: Post by **drgary** » June 13th, 2011, 12:42 am

Today I had a moment to address the damaged heating element contact on my MC. Here's a photo that shows the heating element before starting to try and fix it:

Last week, when Jay (Jaycan) was here, I removed the epoxied bolt that the previous owner told me was only making intermittent contact. Jay suggested digging out the epoxy into the hole and started to do that. I finished using a picking tool to dig out that contact today. You can see the dug-out contact at the left bottom of the photo.

Jay suggested I either use a threaded tiny bolt with female threads on one end and screw it on the tip inside the hole -- he says they sell these in computer stores. I haven't found one yet. I suggested an alternative is to get a small metal tube, heat it so it expands, put it over the tip and allow it to contract to form a grip. Here's a cut-off tiny copper tube I tried for that purpose:

I tried that with a propane torch, and it didn't grip the stud. Can any of you suggest a way to attach a conductor to that broken contact? I think my next step after that's done will be to fill the hole with epoxy and simulate the other heating element terminals. On those, BTW, I'll replace the rusted parts with new ones.

#22: Post by **allon** » June 13th, 2011, 6:55 am

I think you're on the right track with the copper; maybe solder it to the terminal? I know a mechanical connection is preferred for high current. In any case, it will be a little dodgy.

The screws mentioned, btw, are used for holding serial ports and the like to computer cases. They are called "jack screws". For example (random google search):
http://www.rafhdwe.com/jack.htm
They are available with the female portion longer than shown in that example.

As for the epoxy, you might check out this kit:
http://www.orphanespresso.com/Heating-E ... _2823.html

Good luck!

#23: Post by **drgary** » June 13th, 2011, 11:07 am

Thanks, Allon. Those jack screws look like a better way to go. I wonder if solder would come loose on a heating element anyway as opposed to brazing, and I don't know how to braze in that tiny space. And the OE epoxy kit also looks like the way to go.

#24: Post by **drgary** » June 13th, 2011, 11:50 pm

Here's a closer picture of the broken stud. Tomorrow I'll try and fit a jack screw to it. Someone else I talked to today suggest silver soldering but I don't have that gear, so if the jack screw fits and creates a circuit, I'll use OE's epoxy kit to keep it in place.

#25: Post by **orphanespresso** » June 15th, 2011, 3:08 pm

Very difficult repair but you are on the right track. A bit like micro surgery in there. If you need to pick more material out some propane heat on the terminal might soften it so it gets crumbly and picks out easier.

#26: Post by **drgary** » June 15th, 2011, 3:30 pm

Hi Doug,

I think I've figured out a fix. The jack screw suggestion was a good one, especially now that I've found ones with a long nut. I'll try to thread on the nut, first cutting it vertically two ways with a thin cutting wheel so it can work as a threading tool. If it doesn't easily thread on, I won't force things and break off the final piece but may widen out the end a little bit, snug it down, then fill in the inside with some fine wire strands and check the contact. If the contact is solid I'll use the terminal kit you sent me to seal it up with epoxy and finish it off. It is small enough to feel like dentistry.

#27: Post by **drgary** » June 15th, 2011, 6:51 pm

orphanespresso wrote:A bit like micro surgery in there.

Yes, it is! Here's what I've done so far.

I found these jack screws and nuts at Radio Shack for less than $3. I especially like the long nuts. This gives me something to work with.

Before attempting to fasten the modified nut on the stub, I used needle nosed pliers to even out the copper flange surrounding the stub. I did this before trying to fit a nut into that confined space. Now I could eyeball how little room I had to work with.

My next step was to shorten the bolt so it would be a similar height to the other heating element ends. I used a heavy duty cutting wheel to shorten the nut and a regular one, which is thinner, to slot the end.

I cut the end two ways to make those edges and threads act like a threading tool to mate the nut with the stub.

But it was going to be a tight squeeze to avoid a short, so I used a chain saw grinding stone to take off the sharp edges on the outside of the nut and reduce its circumference overall.

Here's the modified nut compared to an original. The flash went off, so sorry if it's a little hard to see.

I then gripped the modified nut in pliers and firmly turned it onto the stub until it created a tenuous grip.

I tested the connection with a multimeter, and it shows a steady reading when touching the new contact and the one below it. So I ditched the idea of inserting wire strands into the hole of the nut.

My next step will be to insert epoxy putty into the space around the modified nut to fasten it in there, make it water tight, and create stable separation between it and the flange. I'll then seal it off with glyptal. The heating element contact kit I have from OE is for my Coffex, so I'll see if I can source from them larger ceramic collars for the heating element ends on the Microcimbali. The threading for a screw remains intact on the contact and it came with mated screws, so it will be easy to attach a tab.

#28: Post by **drgary** » June 16th, 2011, 12:08 am

Finishing up terminal

The last steps were to:

1) seal terminal with heat resistant epoxy from the OE terminal kit; and

2) seal the epoxy with glyptal.

Instructions for this repair and testing with a multimeter are on the OE website here:

http://www.orphanespresso.com/Olympia-a ... 620-1.html

Thanks Doug and Barb!

Next I'll fit a Teflon spacer around the new attachment. The one I have won't go quite around so I'll check with OE about a right-sized one. I'll also need some big Teflon spacers for the Prestina, which is simultaneously being rebuilt.

#29: Post by **orphanespresso** » June 16th, 2011, 6:47 am

Nice work on that terminal. Tedious little job that one. As long as the central circuit cannot touch any of the outer sheath or other parts then it is a success. Don't you love that glyptal? Great smell and nice flowability. I think that insulating collar is going to be another custom job to fit around the nut you installed. Maybe teflon valve packing cord. Or a length of the right diameter teflon tube from Mcmasters. but then you only need 1/8 inch of it and they sell it by the foot. Too bad you don't have the original ceramic bead to file out to fit...just think of some way to guarantee that the connection wire cannot in any imaginable circumstance touch the outer sheath and you have it licked...even a teflon washer cut to fit with a punch, just some effective insulator, even a little rubber sleeve ot prevent, as I said, any possible contact of the metal sheath or boiler base parts to the electrons.

#30: Post by **drgary** » June 16th, 2011, 9:08 am

The "tediousness" was part of the enjoyment of it, trying to solve something like this on a small scale. I didn't mention I also used a thin diamond Dremel bit to further hollow out the flange and make sure the inner contact doesn't touch. What do you think about using Teflon tape sealed with some more Glyptal? Add: For simplicity, I think I just cover it with high temperature epoxy from the same OE kit and cover it with Glyptal.