Could someone please walk me through how to thread holes for the back plate screws on an aluminium enclosure? Is it needed at all? I'm guessing aluminium is too soft to screw into many times, correct? I'm planning on using #6-32 bolts (3,5 mm). Should I drill a 3,5 mm hole then, or slightly larger? And then just put the thread in, maybe with some epoxy?
Quote from: Tobyk on July 24, 2024, 12:22:59 PMCould someone please walk me through how to thread holes for the back plate screws on an aluminium enclosure? Is it needed at all? I'm guessing aluminium is too soft to screw into many times, correct? I'm planning on using #6-32 bolts (3,5 mm). Should I drill a 3,5 mm hole then, or slightly larger? And then just put the thread in, maybe with some epoxy?
All the enclosures I've used have had pre-threaded holes and matching (usually countersunk) screws. A few have been a little tight at first from powder coating overspray. But I've never had to explicitly thread anything. I'm getting mine pre tapped and finished though from stompboxparts.
What enclosure are you (planning to be?) using?
Quote from: tootsMcgee on July 24, 2024, 12:31:29 PMQuote from: Tobyk on July 24, 2024, 12:22:59 PMCould someone please walk me through how to thread holes for the back plate screws on an aluminium enclosure? Is it needed at all? I'm guessing aluminium is too soft to screw into many times, correct? I'm planning on using #6-32 bolts (3,5 mm). Should I drill a 3,5 mm hole then, or slightly larger? And then just put the thread in, maybe with some epoxy?
All the enclosures I've used have had pre-threaded holes and matching (usually countersunk) screws. A few have been a little tight at first from powder coating overspray. But I've never had to explicitly thread anything. I'm getting mine pre tapped and finished though from stompboxparts.
What enclosure are you (planning to be?) using?
Thanks, I should have mentioned that I'm planning to sand cast my own enclusure, not buy one.
There will be a prescribed drill size based on screw size and number of threads and maybe the material you're tapping. Usually an odd size just identified by a number - #36 for a 6/32.
The enclosures I use all seem to use M3.5 x 0.6 thread. The correct drill size is 2.9mm
Though I use 3mm since it's easier to get hold of.
M3.5 thread is also used on UK electrical sockets so repair tools are cheap and readily available (M3.5 tap in a screwdriver handle) I have one in my pedal toolkit in case of overspray/cross threading issues.
Sorry, I can't help with imperial measurements
There are different grades of aluminum. Some are easier to drill/thread than others.
When drilling holes in aluminum use couple of drops of alcohol on the drilling spot/area.
Same applies when threading.
Sand-casting your own enclosures is pretty ambitious! I'll bet you have some crazy shapes in mind. :o
Quote from: stallik on July 24, 2024, 02:15:56 PMThe enclosures I use all seem to use M3.5 x 0.6 thread. The correct drill size is 2.9mm
Though I use 3mm since it's easier to get hold of.
M3.5 thread is also used on UK electrical sockets so repair tools are cheap and readily available (M3.5 tap in a screwdriver handle) I have one in my pedal toolkit in case of overspray/cross threading issues.
Sorry, I can't help with imperial measurements
Thanks, but how can a 3,5 mm thread fit in a 2.9 mm hole? Sorry, new to this..
Quote from: jorg777 on July 24, 2024, 03:29:22 PMSand-casting your own enclosures is pretty ambitious! I'll bet you have some crazy shapes in mind. :o
You bet!😀
Quote from: Tobyk on July 24, 2024, 04:36:37 PMThanks, but how can a 3,5 mm thread fit in a 2.9 mm hole?
3,5 mm is the major diameter (tip of threads), the maximum minor diameter (base of threads) is 2,829 mm. You drill (close) to the minor one and then the tap cuts the threads
around (to the exterior of) that hole.
Quote from: FiveseveN on July 24, 2024, 04:56:57 PMQuote from: Tobyk on July 24, 2024, 04:36:37 PMThanks, but how can a 3,5 mm thread fit in a 2.9 mm hole?
3,5 mm is the major diameter (tip of threads), the maximum minor diameter (base of threads) is 2,829 mm. You drill (close) to the minor one and then the tap cuts the threads around (to the exterior of) that hole.
Thanks, this place is great. I'm not sure we're talking about the same thing here though. I think you are speaking of the act of tapping a hole, correct? This I'm hesitant to do since aluminium is soft. So I'm thinking of using steel thread inserts. Does the same apply to those?
Essentially the drilled hole allows the shank to pass through, then you cut threads with the tap - same shank size.
Are you planning to anodize/hardcoat the cast aluminum? That may help softness issues
Quote from: Tobyk on July 24, 2024, 05:19:55 PMI'm thinking of using steel thread inserts. Does the same apply to those?
Well those come in many varieties, some also threaded on the outside. Though I wouldn't worry about the softness of Al as long as you pick a reasonable diameter & pitch.
You can tap holes in wood and not have problems, no need to overtighten four screws holding a light piece of aluminum fighting the pull of gravity.
Steel threaded inserts are for car engine blocks, not a static wimpy effect box.
Don't over engineer it, just tap the holes, use a drill one size under what the chart says to.
I'm sure I'll be repeating a point already made, but nothing too complicated... Pick the screw you want to use, look up its inner diameter, Drill a hole that size, tap it.
Aluminum is indeed soft, but nothing to panic about, just be careful. The main thing you want to consider is that you are tapping blind holes.. If I were doing this, I would probably opt to do it by hand so I can be slow and deliberate and blow out chips as I go. A spiral flute tap will encourage chips up and out of the hole, but I would make patience and attention your main chip management strategy..
If you're casting your own, you could always fill the hole if you screw it up!
Threaded inserts are a decent backup plan if something goes awry.. I would personally probably just fill with hard marine epoxy and screw into that if I stripped a hole out while tapping, but if you tap it well, you shouldn't have to worry about it stripping later
Quote from: Tobyk on July 24, 2024, 04:36:37 PMhow can a 3,5 mm thread fit in a 2.9 mm hole?
The classic start point is to drill same as the
root of the thread. You can buy combination bits that both drill and tap.
(https://i.postimg.cc/5X4t0Mp4/root-thread.gif) (https://postimg.cc/5X4t0Mp4)
Drill to the root and let the teeth chew the grooves. You may drill a bit over or under-size for easier tapping or better strength.
BTW, combo drill/taps are terrific in heavy sheet metal (240V electrical boxes) but may be a bad choice for blind holes. You need high RPM to drill but then the tap runs too fast and breaks. Anyway they are solid in sets, mostly bigger than pedal-work wants.
In alternate processes like thread-rolling you might drill diameter halfway between tip and root and displace base metal +/- for grooves.
Thanks a lot everyone, guess I won't be needing inserts then. I looked up Hammond enclosures and they are indeed just tapped. Now I'm thinking the hole and thread could then just be made as part of the casting mold, but I guess sand casting is too rough for that to work.. I wonder if Hammond has the tapped holes as part of their die cast molds or if they drill/tap them afterwards..
Does anyone know?
How would they get the mold out of the holes if that were the case?
Quote from: Tobyk on July 25, 2024, 01:45:42 AMtapped holes as part of their die cast molds
Motor-car engine blocks are traditionally cast metal. A big part of the post-casting operations is the drilling and tapping machines.
https://youtu.be/bnb7zXicXsc?t=375
(https://i.postimg.cc/YjRKG6T7/Drill-Flathead-V8.gif) (https://postimg.cc/YjRKG6T7)
(This is the Ford Flathead V-8. If you know the Windsor OHV 289/302/351, it was made on the same machinery with different molds and drills.)
Tap hole sizes vary for different materials.
Usually a slightly smaller drill is used for plastic and aluminum.
Drill sizes determine the percentage of the resulting thread contact.
If you drill with a very oversize drill, the tap will go in easy, sometimes really easy.
If you drill to small, the tap will be hard to turn.
In any case you should turn the tap one turn then reverse some to break the chips.
Else you might break the tap.
Small taps are very delicate.
And if broken ,,, that really sucks.
Depending on what you eventually end up with, this chart might help.
It is primarily used in England.
(https://i.postimg.cc/zL6xB92z/1000001484.jpg) (https://postimg.cc/zL6xB92z)
If I'm interpreting/understanding correctly, you're going to cast a pedal body and screw a piece of sheet-metal to the back (just like a Boss compact pedal, for example)
I'd leave the casting beefy in the corners where the holes need to be tapped;
Stack the parts to gang-drill under-sized holes in both the back-plate and body at once with a drill press to ensure they stay straight. Drilling together ensures correct alignment.
Use a good drill/tap chart (https://www.physics.wisc.edu/ishop/tapdrillchart.html) to size the bit and follow the holes in the body so the threads can be cut;
Tap the holes, a t-wrench will work just fine with a bit of care;
Drill out the holes in the back-plate to the nominal fastener size and cut a countersink as required.
Edit: I searched Amazon for "#8-40 drill and tap" and was returned a two-piece Bosch pack for $7CAD. You should have no problem finding a similar "kit" for any sized hole for very little cost. I'd also like to emphasize "drill press". It is exceedingly difficult to drill holes this small accurately enough to cut snug fitting threads by hand. I paid $20 at a garage sale for a small bench-top drill press that would easily handle this work.
Quote from: ThePracticalPeasant on July 25, 2024, 11:33:07 AMIf I'm interpreting/understanding correctly, you're going to cast a pedal body and screw a piece of sheet-metal to the back (just like a Boss compact pedal, for example)
I'd leave the casting beefy in the corners where the holes need to be tapped;
Stack the parts to gang-drill under-sized holes in both the back-plate and body at once with a drill press to ensure they stay straight. Drilling together ensures correct alignment.
Use a good drill/tap chart (https://www.physics.wisc.edu/ishop/tapdrillchart.html) to size the bit and follow the holes in the body so the threads can be cut;
Tap the holes, a t-wrench will work just fine with a bit of care;
Drill out the holes in the back-plate to the nominal fastener size and cut a countersink as required.
Edit: I searched Amazon for "#8-40 drill and tap" and was returned a two-piece Bosch pack for $7CAD. You should have no problem finding a similar "kit" for any sized hole for very little cost. I'd also like to emphasize "drill press". It is exceedingly difficult to drill holes this small accurately enough to cut snug fitting threads by hand. I paid $20 at a garage sale for a small bench-top drill press that would easily handle this work.
Great info from you all.
Two questions: why is the back plate always sheet metal? Couldn't it be aluminium of the same thickness as the rest of the body? That way I could draw it all in CAD, and have it perfectly lined up. And what about the blind holes, couldn't they also be part of the casting mold, and then I'd just tap them with a t-wrench?
Quote from: Tobyk on July 25, 2024, 11:53:32 AMTwo questions: why is the back plate always sheet metal? Couldn't it be aluminium of the same thickness as the rest of the body? That way I could draw it all in CAD, and have it perfectly lined up.
Price I suspect. And also strength. 20ga would suffice if steel, I suspect you'd need closer to 1/16" with aluminum. This also means the recess for it needs to be deeper...
QuoteAnd what about the blind holes
Tapping a blind hole is no problem so as long as it's deep enough...
Quotecouldn't they also be part of the casting mold, and then I'd just tap them with a t-wrench?
Though I have personally never cast any aluminum, I doubt you'll be able to create a sand mold with enough strength/detail to reliably cast the required hole: likely under 1/8" in diameter, at least 1/2" deep, with walls accurate enough to run a tap into. Not only will that be an exceptionally delicate shaft of sand, I suspect the grain size exceeds the thread-pitch, meaning the sand itself will create inconsistencies that are greater than the size of the thread being cut, requiring the hole to be drilled out anyway. That said, maybe with lost-PLA casting, but a 3D print per casting seems pretty expensive and I doubt would pay back compared to doing it "my way":
Again, assuming it goes together like a BOSS compact stompbox (and assuming you're going to be making these in bulk in some way):
Cast your "top" with big thick corners. Mark the hole positions on one back cover plate and set it in the correct position into/onto the top part. Clamp the parts if you don't have a rabbet to receive the plate. Drill the (four?) holes, undersized, through the cover and as deep as possible into the casting. Stack up your full supply of back-plates with the now-drilled one on top, to gang-drill them all with exactly the same layout. The top one is your master, use it to drill the pilot holes in the rest of the castings. Size-up to the nominal diameter of your machine screws and drill out the rest of the back plates and chamfer the holes. Grab the drill per the tap chart for your machine screws and drill then tap the castings.
No reason you can't have the back-plates laser-cut with the holes drilled and chamfered, or use aluminum if for some reason it works out easier/cheaper for you...
A few things (depending on your experience you may or may not find this useful):
CA glue is your friend when working with metal; the tiniest drop to hold parts together, a bit of heat and they come apart. It might help to make a plywood jig the casting fits into upside down to give it a nice flat face for it to rest on while working. When gang-drilling steel (and possibly aluminum, though I don't know as I have far less experience), if the parts are not pressed firmly together, burrs will develop and push the parts apart which leads to bit wandering, especially with small drill sizes, which in turn leads to an inaccurate representation of the drill pattern, especially deep in the stack. Now that I think about it, making a small plywood box in which two plates can be placed stacked up, might ultimately be faster and more accurate than trying to drill them all at once. If you do have the backs CNC'd in some way, I'd cut/order one that was drilled under-sized and not chamfered for use as a drilling template, as the deeper and straighter a hole, the easier it is to replicate it on the next part...
/two cents
Sounds like fun and a learning experience, I sand casted Al in high school.
You will need a casting box, sand (not playground sand), sprue and riser pins, mallot.
A graphite crucible, a propane oven, crucible lifting tool, gloves, face gear, apron.
Extra set of hands, milling machine to level the bottom, and more.
We cast block and rod shape items, never did thin wall parts and tap holes are not castable.
I would certainly start by casing a simple block.
Quote from: Phend on July 25, 2024, 02:59:45 PMSounds like fun and a learning experience, I sand casted Al in high school.
You will need a casting box, sand (not playground sand), sprue and riser pins, mallot.
A graphite crucible, a propane oven, crucible lifting tool, gloves, face gear, apron.
Extra set of hands, milling machine to level the bottom, and more.
We cast block and rod shape items, never did thin wall parts and tap holes are not castable.
I would certainly start by casing a simple block.
Quote from: ThePracticalPeasant on July 25, 2024, 02:25:55 PMQuote from: Tobyk on July 25, 2024, 11:53:32 AMTwo questions: why is the back plate always sheet metal? Couldn't it be aluminium of the same thickness as the rest of the body? That way I could draw it all in CAD, and have it perfectly lined up.
Price I suspect. And also strength. 20ga would suffice if steel, I suspect you'd need closer to 1/16" with aluminum. This also means the recess for it needs to be deeper...
QuoteAnd what about the blind holes
Tapping a blind hole is no problem so as long as it's deep enough...
Quotecouldn't they also be part of the casting mold, and then I'd just tap them with a t-wrench?
Though I have personally never cast any aluminum, I doubt you'll be able to create a sand mold with enough strength/detail to reliably cast the required hole: likely under 1/8" in diameter, at least 1/2" deep, with walls accurate enough to run a tap into. Not only will that be an exceptionally delicate shaft of sand, I suspect the grain size exceeds the thread-pitch, meaning the sand itself will create inconsistencies that are greater than the size of the thread being cut, requiring the hole to be drilled out anyway. That said, maybe with lost-PLA casting, but a 3D print per casting seems pretty expensive and I doubt would pay back compared to doing it "my way":
Again, assuming it goes together like a BOSS compact stompbox (and assuming you're going to be making these in bulk in some way):
Cast your "top" with big thick corners. Mark the hole positions on one back cover plate and set it in the correct position into/onto the top part. Clamp the parts if you don't have a rabbet to receive the plate. Drill the (four?) holes, undersized, through the cover and as deep as possible into the casting. Stack up your full supply of back-plates with the now-drilled one on top, to gang-drill them all with exactly the same layout. The top one is your master, use it to drill the pilot holes in the rest of the castings. Size-up to the nominal diameter of your machine screws and drill out the rest of the back plates and chamfer the holes. Grab the drill per the tap chart for your machine screws and drill then tap the castings.
No reason you can't have the back-plates laser-cut with the holes drilled and chamfered, or use aluminum if for some reason it works out easier/cheaper for you...
A few things (depending on your experience you may or may not find this useful):
CA glue is your friend when working with metal; the tiniest drop to hold parts together, a bit of heat and they come apart. It might help to make a plywood jig the casting fits into upside down to give it a nice flat face for it to rest on while working. When gang-drilling steel (and possibly aluminum, though I don't know as I have far less experience), if the parts are not pressed firmly together, burrs will develop and push the parts apart which leads to bit wandering, especially with small drill sizes, which in turn leads to an inaccurate representation of the drill pattern, especially deep in the stack. Now that I think about it, making a small plywood box in which two plates can be placed stacked up, might ultimately be faster and more accurate than trying to drill them all at once. If you do have the backs CNC'd in some way, I'd cut/order one that was drilled under-sized and not chamfered for use as a drilling template, as the deeper and straighter a hole, the easier it is to replicate it on the next part...
/two cents
Thanks a bunch, good stuff!
Quote from: Tobyk on July 25, 2024, 03:08:07 PMThanks a bunch, good stuff!
No problem; I'm not much help with the electronomagical parts of all this, but I do have a fair bit of experience with the wood/metal working side of things... ask away and I'll do my best...
Another option (https://www.youtube.com/watch?v=X4Gu2q9W-y0), took me about six hours, is 11ga steel sheet and a FCAW/GMAW welder... and an angle-grinder and a cheap 10" disk sander to cut all the parts... and a die-grinder...
Edit: I just realized you seemed to imply that aluminum allowed CNC, does that mean you possess a router capable of cutting aluminum? if so... I'd build a jig to hold the casting in a repeatable position. First run a program to clean up the back of the casting and cut the step for the back plate then manually place the plate onto the step with a couple drops of CA glue and run the drilling and chamfer programs. I suspect that given the thicknesses at play, you could drill to the tap size then cut the countersink deep enough into the backing plate to widen the hole to fit the nominal size of the screw, without requiring the second drilling steps and associated risks or removing the backing plate from the casting that serves as it's fixture. Touch the plate with a torch to burn the CA glue, lift the lid off, and run the tapping program (or tap manually). Remove the casting, pair it with its lid, and repeat the whole thing as necessary.
Quote from: Phend on July 25, 2024, 02:59:45 PMsand (not playground sand)
No, special sand.
When I was young this was fairly easy: there was a casting shop in every third town. Go in with a strong bucket, say it is a school project. Today: as it happens there was a boat propeller rebuild (polish your erosion to recurve the whole prop) shop a few towns over from here, but I think they just moved south.
You might do bad work mixing mason sand with molasses?
Quote from: PRR on July 25, 2024, 08:41:14 PMYou might do bad work mixing mason sand with molasses?
hahaha!
It's slightly overpriced, but you can buy Petrobond on Amazon...
Do not forget to include you logo/name on the "pattern" , remember to make it mirrored, maybe.
Quote from: Phend on July 27, 2024, 05:19:59 PMDo not forget to include you logo/name on the "pattern" , remember to make it mirrored, maybe.
Had that in mind. Don't believe it need to be mirrored in the model, it will be in the sand though!