Snapped screws - Welded standoffs - DPO

[The Dude]

Maybe just remove the welded standoffs that have broken off screws in them and install new threaded standoffs of the appropriate size with screws.

[NateS]

Stripped bare, ready for some heat. I must say that I'm impressed with the chassis design - this looks like it was tailor made for DIY. There's three parts that are each largely flat sheets with single plane bends. Front panel, lid, and chassis. The chassis is bent into a C and has lips along the side to fasten the lid, but you could make the entire chassis on a leaf brake. I think I'll be borrowing this in the future.

[Bloomfield]

It sounds like you have everything stripped out ready to use a torch. I guess I'm a bit late here but if you have a big soldering iron, like 90-150W, that would probably get them hot enough to break the Loctite. If you sand/grind the part to expose bare steel, you can tin some solder on to improve the heat transfer. Good luck with it.

[NateS]

pencil torch and left handed drilling didn't break them loose. I'm going to try slotting next, then chopping them off low enough to hopefully get past the screw but still having a hole to locate off of. I did try my soldering iron, but it's a delicate electronics iron. Had I access to a big stained glass window iron then we might get somewhere, but my little sparkfun Hakko clone won't touch it.

[nevetslab]

There is quite a bit of mass in the inductors heat sinks and transformers. This definitely should not float.

The old Benzo-Matic torch is what I normally use for a shop blow torch. I suppose in a pinch, you could use stick matches and hair spray to make a blow torch, though it's very wide flame, hard to control. Maybe change tips in the hair spray, using one from a can of W-D 40 with the nozzle, so the flame would be much finer?

[g1]

WSTA2 Pyropen Jr. or similar butane solder iron that you can run without tip are great for getting into tight spots.
Even with the tip on, the Pyro Jr. will do almost 850 degrees. Torch about 2350.
Some of the much cheaper competition would probably do similar.

[olddawg]

You also may be able to drill them out from the back side and simply put a screw through the hole with a nut in the top.

[NateS]

I turned a centering bushing on the lathe. The closest size up from the boss ended up giving me about 0.005" clearance, and I drilled the through hole undersize, then finished up with the left handed 3/32" bit I was going to use. Left handed drilling didn't do anything, so I decided to save my new lefty bits and switch to right handed bits. Glad I did - I got almost through and I snapped it. But the jig worked marvelously - even for ones I'd started by hand yesterday and were badly off center. I had about two holes that I need a longer bit to reach, and two I need a right angle head for, but otherwise it seems to be working. I drilled them to 3/32 as this was the biggest size I had that was just under the minor diameter of a 3mm-0.5mm screw. I'm going to try tapping these, but failing that I'll just use the center holes to drill through and put flat heads into a through threaded hex standoff.

[nevetslab]

I turned a centering bushing on the lathe. The closest size up from the boss ended up giving me about 0.005" clearance, and I drilled the through hole undersize, then finished up with the left handed 3/32" bit I was going to use. Left handed drilling didn't do anything, so I decided to save my new lefty bits and switch to right handed bits. Glad I did - I got almost through and I snapped it. But the jig worked marvelously - even for ones I'd started by hand yesterday and were badly off center. I had about two holes that I need a longer bit to reach, and two I need a right angle head for, but otherwise it seems to be working. I drilled them to 3/32 as this was the biggest size I had that was just under the minor diameter of a 3mm-0.5mm screw. I'm going to try tapping these, but failing that I'll just use the center holes to drill through and put flat heads into a through threaded hex standoff.

That's a nice centering drill jig you machined! I forgot to ask....are the standoffs thru-hole or blind hole? Are you going to re-tap for M3, or change to a US thread size. 3/32" is just slightly oversize for #4-40, but still within limits, though you'd be dealing with the M3 thread pattern being left over. #4-40 is deeper pitch. #6-32 would allow eliminating all hints of the M3 thread. Hole size for #6-32 is #36 (0.1065" dia).

[NateS]

They're blind. If they were through holes I'd have drilled and retapped from the bottom, easy peasy. I got a right angle head this morning - it's hex shank only, not a drill chuck, but they didn't have any other options that didn't involve buying an entire drill in a system other than the one I'm invested in. (All my cordless tools are Ryobi One+ Batteries. I wasn't about to buy a tool in another system, and they didn't have any corded RA drills that werent $200 or way too big to fit.)

The longer bit for the two holes near the folds I haven't tried yet but the longest 3/32 I could find was a 1/4" hex shank. They did have some superlong bits in 1/8" but that's too big, and I'd have to make a new bushing. (My tailstock doesn't clamp tight enough to drill - so that took way longer than it should've.) If I break anything more I'm just going to redrill for #6-32. It might be necessary anyway - I hadn't really considered that retapping with the same size is likely to turn it all to mush unless the tap magically seeks the old threads. I can see drilling a rod stuck inside another rod seeking center but I kinda doubt the tap has magical self-seeking properties.

[NateS]

Right angle head plus bushing worked like a charm for the remaining holes. Drilled everything to a #36 hole for a #6-32 tap, except for the ones I needed a right angle head to reach. Those I had to drill 7/64th because that's the next smaller hex shank bit I had, but hopefully I can pin vise drill those to tap size, no more metal than remains.

Now to contact Stew-Mac to sell my PEM self-clench nut centering redrill bushing for $65.

[NateS]

Had to tap the low clearance hole from the bottom. Drill came out square in the middle of the "caution" label, so I titled this one "Screw Caution"

[NateS]

Bah humbucker. 6-32 won't go through the screw holes in the board. I have through holes, but 0.065" pcb + 0.060" sheet metal + 0.25" standoff divided by two...

My options seem to be 1) replace standoffa with double female and screw to the chassis from underneath. 2) drill pcb (yuck. Fiberglass, highest risk to killing the amp.) 3) take up the difference between 6-32 and 4-40 with epoxy/solder/CA glue.

The landing is huge. I don't think I would hit any internal traces. But it's hard stuff that destroys bits and the board is floppy under it's weight. Don't like the idea of that thing on my drill press. Maybe that's my best option and I'm just skittish

[nevetslab]

Bah humbucker. 6-32 won't go through the screw holes in the board. I have through holes, but 0.065" pcb + 0.060" sheet metal + 0.25" standoff divided by two...

My options seem to be 1) replace standoffa with double female and screw to the chassis from underneath. 2) drill pcb (yuck. Fiberglass, highest risk to killing the amp.) 3) take up the difference between 6-32 and 4-40 with epoxy/solder/CA glue.

The landing is huge. I don't think I would hit any internal traces. But it's hard stuff that destroys bits and the board is floppy under it's weight. Don't like the idea of that thing on my drill press. Maybe that's my best option and I'm just skittish

Your PCB thru-holes must be at least 0.125" dia. I'd use a tapered reamer to enlarge the holes. You must have clearance on the bottom side of the PCB to accommodate the standoff (must be at least 0.25" dia), as well as the head of the screw on the top side. Now, I've drilled fiberglass PCB's for years and never had issues, but, then I have a full set of Fractional & Number drills, and a number of Letter drills, and a full set of Taper Pin reamers, which have a much smaller range from the start & stop size on each numbered reamer (they are shaped to that of the Taper Pins sizes), and work great for this sort of application.

If you don't have a tapered reamer, I'd invest in one for this task. Keep the process with hand tools rather than risk it on the drill press. I've also chucked drills into my Collet T-Handles where I usually put my taps. You CAN use the appropriate drill shank in the T-Handle and run it thru by hand. Cuts nicely, assuming the drill bit is sharp.

[NateS]

Clearance hole for a #6 screw is nominally 0.150, I measured my holes at about 0.120. My screws were just a hair under 0.136 which was a drill size I had. I was able to spin a drill bit in a pin vise through in a few turns by hand, and all the holes line up - I really expected some tolerance issues cutting it that close to actual dimensions but it seems to have worked. I'm about 2 screws short of buttoning it back up once I find that last bag, (and fighting with trying to crimp JST connectors) and it's done.