Tap & Die help needed please.

Yeah, so I'd like to cut some fresh new thread beyond the existing thread on my cambered bolts for reasons I will reveal later.

After Googling around I now know I will need a tap & die set to create new thread, but to get to the unthreaded section at the end of the bolt I must pass over existing thread.

OK, so I watched a self help Youtube video on how to do this but the guy in the video advises against using a die on existing thread. Therefore I'm guessing I will need both a die and a rethreader to repair the first section of thread I damaged using the die...if that makes any sense.

Are you still with me ?..... Somebody wake up Hicks. :alien:

I did a search on what tools I would need to do a die and re-thread but I'm a bit confused with their jargon. Here's what I'm looking at with regards to the tap & Die set (description below) > 45pc Jumbo Metric Tap & Die Set

45pc Jumbo Metric Tap And |Die Set
National Coarse and Fine Threads
M6 - M24
Large sizes in taps, large sizes in dies
Heat treated tungsten alloy steel
Sizes of combination set:
1½" OD:
M6 x 1, M6 x 0.75, M8 x 1.25, M8 x 1,
M10 x 1.5, M10 x 1.25, M12 x 1.75, M14 x 2, M14 x 1.5
2" OD:
M20 x 2.5, M20 x 1.5, M22 x 2.5, M22 x 1.5, M24 x 3, M24 x 1.5
Consisting of:
20 taps - 20 split dies (adjustable)
2 tap wrenches
Small (M6 to M12) - Large (M8 to M24)
2 x 2" diameter die stock with (1½) adaptor
1 screw driver
presented is steel case

Two things in the above description confuse me. 1st) What is meant by National Coarse and Fine Threads ? ...2nd) Which of the two M20 dies do I need, M20x 2.5 or M20x 1.5 and why are there different sizes ?

Any tips on tap & die + rethreading much appreciated. Thanks

Quote: Originally posted by soliver

I did a little search regarding tap and die designations in the metric arena. Here in the states we have designations for our tap and die sets that would say something like 1/4-20 which means the outer diameter (OD) of the bolt or inner diameter of the nut (ID) is 1/4 inch and the 20 is the thread count per inch (TPI) so a 1/4-20 die would cut 20 threads per inch on a 1/4 rod. It appears from what I could find from a brief search is that it is a similar designation in the Metric arena. From what I can tell the second number in the designation for metric tap and die is the pitch of the thread, so a M20x1.5 would cut threads on a 20 mm rod at a shallower pitch than an M20x2.5 ... So it's just a guess that the M20x1.5 is a finer thread than the M20x1.5. And I've only ever threaded mild steel and all I can tell you is lube, lube, lube.

Thanks for your time.
I had the idea that those last numbers might be the nut size to fit onto the rod. Your explanation makes more sense. I'll do a search along those lines, now I know what to search for.
Lube up, good tip.

Ok thanks all. Go slow, back off and plenty of lubricant. Use coarse thread. M20x2.5...got it.
I don't have a workbench vice but the cambered bolt is tightly bolted to the bug so should be ok do you think ?

The cambered bolts are stainless. From what you say soliver, this will be tough going.

Here's a picture of the cambered bolts and what I want to do with them.

Quote: Originally posted by TEDWESLEY

The first thing that you need to determine is whether the current threads were rolled or cut. A rolled thread is larger in dia. than the stock it is rolled from. Since you will be cutting threads, this means that you will not have full thread depth when you cut the thread with a die. Keep that in mind when you are torqueing the nut as you may strip the threads. Using the die is relatively simple. Thread the die on to the existing threads until you reach the unthreaded portion, using lubrication ( Crisco shortening will work ) advance the die a quarter turn, then back it off a bit and do another quarter turn etc. until you have the thread length you need. Note that the die has two sides, the stock feeds into the wider tapered side. Go slow and all should come out fine,

Thanks! I appreciate your help. It seems like there's a good chance that I could end up ruining these bolts. I'm starting to think that John' advice above would be a whole lot simpler. I should get these done professionally or drop an email to ptw and ask him to make me another set. I was hoping to do this myself without bothering anyone but reading your advice makes me think that I may be out of my depth as I have zero experience.

...or on the other hand, a useful skill to learn. Need to sleep on it.

Quote: Originally posted by Chook

A few washers or a sleeve on the outside (or inside) of the wheel would fix your hassle maybe? The hard work has been done (getting the die to start correctly/square) and adding more thread should be doable. As TEDWESLEY said, the rolled thread will be slightly larger, than what you will cut. Your V in the thread you cut will be shallower. I would be surprised if it would make a lot of difference though, as it is not caring a huge structural load like most 20mm bolts do. Lots of lube and go for it, but in a vice as some serious elbow grease will be needed. A good quality die will be a given. Most engineering shops would probably do the job, for the cost of the die alone.

Thanks Chook, loving the avatar. I did try a spacer on the bolt but the wheel I wanted to use (oops, given away my secret) ended up being too far out and imagine the bolt could bend under the increased leverage.

soliver, I'm going to speak with a guy tonight who runs a machine shop close by and see if he or someone he knows else can help.

Thanks to everyone for your advice. I hope that someone braver than me at some future date will benefit from all the knowledge in this thread.
I would have liked to have given this a go but with no tools or vice and no experience the smart way as you're all suggesting is to get this done professionally and I agree.