A question for machinists (tap/die related)

billbillw

I have an older (90's) audio rack that had casters installed on it when I received it, but one of them broke off and now I would just like to fit it with spikes. I took the part to the hardware store and found the only one that seemed to fit was #12-24, but it seemed a bit sloppy.

However, here is my question. I would like to enlarge/re-tap the hole fit 1/4"-20 which is more of a standard for spike sizes. Do you think there is enough material (I'm pretty sure its steel) left in the hole to get good threads or are the two sizes too close?

thsmith

Not a machinest but a #12 = 0.189 and the drill size to tap a 1/4" hole is #7 bit = 0.201

Cutting it pretty close

billbillw

I knew it was close, that's why I was looking for someone with experience. Don't have much choice since I can't find any spikes that are strong enough in a #12-24 thread.

dkg999

It could possibly be a metric size if the 12-24 size is a sloppy fit as I believe you referenced. I had a similar issue with some threaded holes in the stand for one of my sanders and I just spread some JB Weld good and thick to fill the old metric threads and then retapped for the screw size I had on hand. It didn't have to hold the type of weight you would have on the feet of an audio rack, so not sure the trick would work in your application.

billbillw

dkg999 wrote: »

It could possibly be a metric size if the 12-24 size is a sloppy fit as I believe you referenced. I had a similar issue with some threaded holes in the stand for one of my sanders and I just spread some JB Weld good and thick to fill the old metric threads and then retapped for the screw size I had on hand. It didn't have to hold the type of weight you would have on the feet of an audio rack, so not sure the trick would work in your application.

Its not metric. Metric 5mm fits more sloppy than the #12 and 6mm doesn't fit at all. (makes sense because #12 is slightly less than 5.5mm).

BIZILL

off the top of his head, my cnc setup guy at work says you should be fine re-tapping to fit 1/4-20. but that was off the top of his head. depends on major and minor diameters of the threads, which i don't have a bolt in front of me nor can i readily jump online for reference. stuck at work and can only post from my cell so i pretty much only keep two windows open and polk is one of the windows.

ps, he mentioned he's never heard of much that takes a 12-24 and to be certain it's not 10-24'

billbillw

BIZILL wrote: »

... he mentioned he's never heard of much that takes a 12-24 and to be certain it's not 10-24'

I'm certain. I spent 15 minutes at the hardware store trying all the different sizes. #10 just slid in. 1/4-20 couldn't get past the first thread. M5 sloppy, M6 too big. #12-24 is it. I know its uncommon, that is why I want to convert it.

I really want to put some of these on it (cheap I know, but should do the trick)
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=249-727

Since they are steel, they should be strong enough to hold 200-300 lbs of equipment.

dkg999

Even if the new threads are not completely the way they should be, if you can use a washer between the new feet and the rack post that lets the weight be distributed from the threads to the shoulder of the spike, it might work.

billbillw

dkg999 wrote: »

Even if the new threads are not completely the way they should be, if you can use a washer between the new feet and the rack post that lets the weight be distributed from the threads to the shoulder of the spike, it might work.

Thanks for that idea. Looks like I'll be picking up a tap set...

billbillw

Keiko wrote: »

Larry, TOOLFORLIFEFAN is a machinist. He may be able to suggest something also, Bill.

I'm pretty sure this idea will be fine. I might get in touch with Larry for something else I have in mind though.

gdb

Pics would be a big help !

billbillw

gdb wrote: »

Pics would be a big help !

A photo of a hole would help? Its just a threaded hole and I'm looking to make it bigger.

gdb

The surroundings of the hole/ how much material is there to work with /etc/etc:rolleyes: If you knew you had the space, why'd you even bother asking your question? Cripes....thread it for 1/2-20 using a 29/64 bit, then you'll be able to really load up that rack!

billbillw

gdb wrote: »

The surroundings of the hole/ how much material is there to work with /etc/etc:rolleyes: If you knew you had the space, why'd you even bother asking your question? Cripes....thread it for 1/2-20 using a 29/64 bit, then you'll be able to really load up that rack!

Rolleyes? Grow up.

Look, I didn't really think there was a need for a photo. The early posters seemed to know exactly what I was talking about. I know there is plenty of material. It is a large 1" round, 1" thick disc of steel that has threaded holes on the top and bottom. One side is threaded to 3/8"-16 and fits the threaded rod for the rack. The other side has a small hole (#12-24) that previously had a caster screwed into in it.

I wasn't concerned about whether there was enough material, but whether #12-24 was too close in size to 1/4"-20 to be able to properly drill it out and have clean metal for the 1/4" threads.

The reason for not going larger is the lack of cheap, available spikes. Most affordable off the shelf cone spikes are 1/4"-20 or M6.

Polkersince85

The major diameter on a 12-24 thread will run between .207 to .215 in. The minor diameter of a 1/4-20 will be .196 to .207 in. Your retreaded hole would have flattened threads but still would probably work. You would need a precise setup with rigid drillpress to get the hole on center. Personally, I would go for a 3/8-16 UNC if you can find spikes for that size.

gdb

mea culpa. good luck !:)

billbillw

Polkersince85 wrote: »

The major diameter on a 12-24 thread will run between .207 to .215 in. The minor diameter of a 1/4-20 will be .196 to .207 in. Your retreaded hole would have flattened threads but still would probably work. You would need a precise setup with rigid drillpress to get the hole on center. Personally, I would go for a 3/8-16 UNC if you can find spikes for that size.

Now that's what I was looking for. Hmm, maybe back to the drawing board.

Polkersince85

Any way you could thread the 3/8 thru and just screw the rod out the bottom?
Maybe you should read the current "Guy" thread.

billbillw

Polkersince85 wrote: »

Any way you could thread the 3/8 thru and just screw the rod out the bottom?

The threaded rod is a certain length which matches the outer tubes (rod inside of tube) so not much left to extend beyond the lower shelf. Might not make sense, but think of it like a flexy rack, but with tubes over the threaded rod. The tubes are both cosmetic and stabilize from swaying.

The lower disc is really just cosmetic. If I really had to, I could just use a 3/8" coupling nut with a washer on the bottom instead of the disc and go from there. It would look pretty bad though.

Polkersince85

You should be able to just tap the threaded hole with a 1/4-20 tap. The major and minor diameters are close. The threads will look wierd but the 1/4-20 would dominate. May wooble a bit. Just start the tap as straight as possible and use some oil. Remember to turn the tap in a circle, not sideways. If it doesn't work, just go bigger.

billbillw

Polkersince85 wrote: »

You should be able to just tap the threaded hole with a 1/4-20 tap. The major and minor diameters are close. The threads will look wierd but the 1/4-20 would dominate. May wooble a bit. Just start the tap as straight as possible and use some oil. Remember to turn the tap in a circle, not sideways. If it doesn't work, just go bigger.

Thanks. Might try that. Wouldn't be out much if it didn't work. Those cones from PE are only 50c each so its worth a try.