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I just bought some tappable aluminum tubing to make nose tubes/chassis braces for my BME chassis. What size tap do I need for the screws in the front and side?

Anyone have a good online source for cheap individual taps without buying a set? I plan to look at Lowe's and another hardware store this weekend.

4-40 and I buy mine over at the local hardware store.

Sears usually has these. Lowes probably won't have anything that small.

Lowes has them I bought one yesterday, came with a drill bit for under 5 bucks its a Kobolt brand.

Any hobby shop should have them, especially with a K&S or Dubro rack, they should be about $5. Harbor Freight, tool/machining supply stores will have them too (I had to get a 3mm tap from the latter). And tooling website will have them too. The hobby ones sometimes come with a drill bit, but the K&S tubing (guessing that's what you bought?) doesn't really need to be drilled first. Just use a drop of light oil on the tap.

Get yourself a t-handle, also pretty cheap. For softer materials like plastics you can also use a screwdriver-shaped collet. I ended up using a big one meant for holding needle files, some low-quality foreign-made thing I got cheap at a model train show. Slip the tap into a piece of fuel tubing to keep the threads clean and sharp when not in use.

Flush out the hole to get rid of the oil and shavings when you're done. With a cutting tap the fit will be 'loose', like the plain metal nuts, so light thread lock or Goop or something isn't a bad idea. You can get non-cutting taps, but I haven't tried one yet. I tapped all the holes in my Tamiya F-350 for M3 screws, and the fit is loose until you snug it, so next time I'll try the forming tap.

Now if only I could find a tap that works with the threads on the Associated turnbuckles, I could thread and JB Weld the right-hand end of a short turnbuckle into the K&S tubing and make turnbuckles for a crawler.

the associated turnbuckles are probably 4-40 or 3mm. Mcmaster-carr sells left handed taps, I believe in both those sizes.

jwscab wrote:the associated turnbuckles are probably 4-40 or 3mm. Mcmaster-carr sells left handed taps, I believe in both those sizes.

I can't seem to thread a 4-40 nut onto the right-hand thread of one. They might be 5-40, but they are definitely not metric. The idea is to thread the right-hand thread into the tubing, leaving the lefthand thread exposed and making that one end of the turnbuckle. Then put a length of threaded rod into the other end, making a long tie-rod out of the whole thing.

yeah, 5-40 is also used by associated in a few places. should still be a size carried by mcmaster. you can get all-thread, or some long screws and clip the heads off for the other end. use jamnuts and red loctite on both sides, and they should work out very well.

Thanks everyone!

I'm going to hit up Lowe's and Sears tomorrow. I actually have two complete tap & dye sets, but nothing as small as I need.

jwscab wrote:yeah, 5-40 is also used by associated in a few places. should still be a size carried by mcmaster. you can get all-thread, or some long screws and clip the heads off for the other end. use jamnuts and red loctite on both sides, and they should work out very well.

Actually, looking on McMaster for taps, they must be 4-48. #4 is the screw size (0.1120" nominal size), 40 is the number of threads per in (8-32 is obviously a bigger screw, with a coarser thread). 4-48 would be the same diameter, but would be a finer screw thread, which makes sense since it takes more turns to screw it in, giving finer adjustments. The threads on a slipper clutch, aluminum front axles, or the bellcrank screws, would be 5-40, which is why the nuts kind of work on a 4-40 screw, but not the other way around.

http://www.mcmaster.com/#taps/=6axx2g

A ratcheting t-handle would be really nice to have. Pay attention to drill bit sizes, so you don't end up with a sloppy hole (won't stay tight, will strip easily) or one that's too tight (can break the tap).

http://www.marfas.com/machinescrewtapping.shtml
http://www.mcmaster.com/#taps/=6axx2g
http://bobmay.astronomy.net/misc/drillchart.htm

If you want to get really geeky:
http://new.industrialpress.com/products/category_feature/MH
It takes years to become a good machinist, I think most of that time is spent learning to use the Machinery's Handbook.