clarnibass
Aluminum
- Joined
- Dec 23, 2015
Not exactly a helicoil...
I repair musical instruments and have this one for repairs. The "triplet post" (the bar with three small threaded holes in it) is attached to the (wood) clarinet with two screws (on top, which you can see). The thread is stripped (in the wood). The screws are 1.75mm diameter and 0.6mm pitch. The clearance holes were 1.8mm. I enlarged them slightly to 1.9mm and used longer 1.9mm diameter screws, also 0.6mm pitch. Unfortunately the threads in the clarinet body are ruined enough that it didn't help. One kept turning and the other felt like it's about to strip.
Some problems like this are fixed by a few methods using various types of inserts that in this case won't work well. I think I'll make a metal inserts (likely nickel-silver, maybe brass), threaded and Loctite to the body, with inner threads for the screws to go into (I'll make other screws instead of the non-standard M1.75x0.6mm ones, which look a bit like a "tweener" metal/wood screw shape). A bit like a helicoil in purpose.
The screws only really need to hold the part to the body, it's the flat bottom and the shape of the part and the cutout in the wood that hold it in the correct position for alignment.
The thing is, I've never made a part like this in such a cramped area. If the inserts are too large, they would stick out and get to the hinge tubes of the keys themselves, not allowing them to move (plus sticking out of the wood and looking ugly).
I could make the inserts completely off the instrument, then thread them in. Or I could drill and tap, or just tap, in situ.
I'd probably go for M1.8x0.35mm, or maybe 1-64 or 1-72 for the inner threads (and the screws). Question is then how small can the outer threads be, without compromising the wall thickness too much. I would want it as small as possible in this case.
I guess it could be slightly smaller if I tap the inner thread once installed, but not sure it's not too much of a risk (e.g. depending on wall thickness, might just strip the wood again, even if Loctited in place).
If I drill in place too, maybe it could be even smaller, but drilling this way is also a little tricky, risking the wood stripping, plus harder to keep it exactly perpendicular (though it doesn't have to be very accurate).
So first I'm trying to see what's the smallest thread I could use for the outer diameter, without the part itself being ruined by making it off the instrument (i.e. the part collapsing from the second threading operation, now being too thin). Also whether there's a significant difference to that risk by drilling/turning and tapping the inside or outside first.
Thanks
I repair musical instruments and have this one for repairs. The "triplet post" (the bar with three small threaded holes in it) is attached to the (wood) clarinet with two screws (on top, which you can see). The thread is stripped (in the wood). The screws are 1.75mm diameter and 0.6mm pitch. The clearance holes were 1.8mm. I enlarged them slightly to 1.9mm and used longer 1.9mm diameter screws, also 0.6mm pitch. Unfortunately the threads in the clarinet body are ruined enough that it didn't help. One kept turning and the other felt like it's about to strip.
Some problems like this are fixed by a few methods using various types of inserts that in this case won't work well. I think I'll make a metal inserts (likely nickel-silver, maybe brass), threaded and Loctite to the body, with inner threads for the screws to go into (I'll make other screws instead of the non-standard M1.75x0.6mm ones, which look a bit like a "tweener" metal/wood screw shape). A bit like a helicoil in purpose.
The screws only really need to hold the part to the body, it's the flat bottom and the shape of the part and the cutout in the wood that hold it in the correct position for alignment.
The thing is, I've never made a part like this in such a cramped area. If the inserts are too large, they would stick out and get to the hinge tubes of the keys themselves, not allowing them to move (plus sticking out of the wood and looking ugly).
I could make the inserts completely off the instrument, then thread them in. Or I could drill and tap, or just tap, in situ.
I'd probably go for M1.8x0.35mm, or maybe 1-64 or 1-72 for the inner threads (and the screws). Question is then how small can the outer threads be, without compromising the wall thickness too much. I would want it as small as possible in this case.
I guess it could be slightly smaller if I tap the inner thread once installed, but not sure it's not too much of a risk (e.g. depending on wall thickness, might just strip the wood again, even if Loctited in place).
If I drill in place too, maybe it could be even smaller, but drilling this way is also a little tricky, risking the wood stripping, plus harder to keep it exactly perpendicular (though it doesn't have to be very accurate).
So first I'm trying to see what's the smallest thread I could use for the outer diameter, without the part itself being ruined by making it off the instrument (i.e. the part collapsing from the second threading operation, now being too thin). Also whether there's a significant difference to that risk by drilling/turning and tapping the inside or outside first.
Thanks