HSS taps vs carbon steel taps

[Gody]

Being european, I used to use metric sized screws for my folders but since there are a lot more different screws available in the imperial sizes, I recently made the switch to american screws, and purchased a load from USA Knifemaker. Furthermore, the 1-72 carbon steel taps where about 30% the price of the HSS M2 (2mm = .080 inch) and even the screws were much cheaper.
Today I was tapping .080 titanium for 1-72 screws, drilled with a 1,6mm drill, which is quite a bit bigger than the recommended #ed drill. I thougt I was quite carefull but I broke the carbon steel tap on the first hole. I felt quite a lot of resistance trying to cut the thread. I then decided to try the M2 HSS tap, which is about 11 % bigger than the 1-72, using the same 1,6mm drillbit for the holes. The M2 tap went through the holes like it was butter, and resistance felt much less.
I used a battery power drill and drove the tap through in one continious pass.
Both taps were tapered and seems to be of the same type, apart from the material.

My question therefore is:

Are Hss taps so much better than Carbon steel and are they worth the extra price (about 3 times as much)?
What kind of taps are the rest of you using?

Brian

 

[machinistbutler]

They are worth the price. Snapping a tap off can ruin a piece that you have spent alot of time building. The hss generally cut nicer threads, and you can get different qualities of hss, the cheap chinese so called hss are probably crap. The last tap I bought in march cost $400, but it did a good job.

 

[Gody]

Thats what I suspected, but apart from price, how do you determine the quality of a tap? Jantz, Texas Knife, and USA Knifemaker among others, all offer HSS taps in the 9-11$ range (which is a far cry from your 400) but will they be a marked improvement over the carbon ones?

Brian

 

[machinistbutler]

I will have to look at work for the brands that I use, a good one will cut like butter, almost no effort with the small taps up to 3/4 inch. Use rapid tap or a good tapping fluid helps alot too. This tap wrench is about six feet across, the tap in it is the one I bought most recently.

 

[timgunn1962]

Just about all of the HSS taps have ground threads, whereas many of the Carbon steel ones have cut threads. Side-by-side, the difference in quality is usually very obvious.

Largely it's a case of getting what you pay for and yes, good taps are well worth the extra money.

 

[PT Doc]

A machine shop owner that I know uses hss taps from Japan. He gave me one knowing that I would be tapping 3/8 x16 in 1/2" steel. He also recommended using some kind of green cutting fluid that is biodegradable that he gave me and he thought that I should not have any problems. He also recommended that I undersize the final hole a bit so that I have more thread in the newly tapped hole.

 

[javand]

I use Drillco taps, and drills. A local industrial supplier carries the line as their premium domestic option and turned me on to them. They're excellent quality. Prices through them were much lower than the retail prices listed on Drillco's site also. I've been incredibly pleased with the quality of the nitro drills, and their hss taps, especially compared to anything else I've tried. Their small drills and taps are usually cheaper than buying crap ones elsewhere, but the larger sizes can get expensive fast.

 

[A C Richards]

A machine shop owner that I know uses hss taps from Japan. He gave me one knowing that I would be tapping 3/8 x16 in 1/2" steel. He also recommended using some kind of green cutting fluid that is biodegradable that he gave me and he thought that I should not have any problems. He also recommended that I undersize the final hole a bit so that I have more thread in the newly tapped hole.

Do not cut an undersized hole. Well if your talking .001or.002 it will not make that much difference but use the drill suggested for your tap. In your case a 5/16 is the suggested hole size. A tap will not gain much in thread strength if you decrease the hole size, but it will greatly increase the pressure required to cut. This is the major cause of broken taps there is, next to not using a guide. If you are single point cutting or mill cutting a thread then yes leaving a little additional thread is ok since it will not cause undue stresses. The green thread cutting fluid did not work for me at all and in SS it was worse than nothing at all. Rapid Tap is great fluid as is number1 gold. Used them both and rely on them still. If you are doing to really heavy cutting or many many holes then Moly Dee is my suggestion. It smells really bad but preventing one broken tap is worth any annoyance.

 

[PT Doc]

Do not cut an undersized hole. Well if your talking .001or.002 it will not make that much difference but use the drill suggested for your tap. In your case a 5/16 is the suggested hole size. A tap will not gain much in thread strength if you decrease the hole size, but it will greatly increase the pressure required to cut. This is the major cause of broken taps there is, next to not using a guide. If you are single point cutting or mill cutting a thread then yes leaving a little additional thread is ok since it will not cause undue stresses. The green thread cutting fluid did not work for me at all and in SS it was worse than nothing at all. Rapid Tap is great fluid as is number1 gold. Used them both and rely on them still. If you are doing to really heavy cutting or many many holes then Moly Dee is my suggestion. It smells really bad but preventing one broken tap is worth any annoyance.

5/16 is .3125. He recommended 0.302. I'll be using a drill press and according to the drill press chart I should have enough slowness since I can slow down to 300 rpm. Thanks for the good info before I start the tapping.

 

[A C Richards]

If you are only tapping 1/2 inch then It should be OK. Drilling with a DP is ok. Tapping under power can be an experience. Since the top of a 3/8 tap is smaller than the cut you could possibly pull it off. Just will your threads clear the back before the chuck hits the work? I would recommend hand tapping for the first few anyway. Good luck.

 

[Nathan the Machinist]

.302 is not the correct hole size to tap 3/8-16. As Chuck said, you want 5/16. There is nothing to be gained by under sizing it, and the cutting forces go way up. You'll get best results using the correct hole size.

Power tapping on a 3 phase machine where you can reverse on the fly is no big deal. Power tapping on a single phase drill press that can't be instantly reversed is another story.

 

[PT Doc]

.302 is not the correct hole size to tap 3/8-16. As Chuck said, you want 5/16. There is nothing to be gained by under sizing it, and the cutting forces go way up. You'll get best results using the correct hole size.

Power tapping on a 3 phase machine where you can reverse on the fly is no big deal. Power tapping on a single phase drill press that can't be instantly reversed is another story.

Ok, sounds like hand tapping will work out better on a 5/16 hole. Thanks for the recommendations everyone.

 

[Gody]

Thanks everyone for your valuable input. I´ll go shopping for some HSS taps.

Brian