An exercise in futility!!!!!!

[Dixieblade57]

I am in the process of building a 2x72 clone for grinding blades. I decided to tap the 1/2"thick side plates that make up the tube for the tooling arm for 10-24 flat head machine screws. In retrospect maybe I should have went to a larger diameter. :jerkit:

I am sure I am using the right size drill bit as I originally bought the titanium nitrate coated bit and tap combinations from Lowes, to work with. I think I am have broken number 4 of them and 2 plain high carbon steel 10-24 taps from Irwin. They were all what is called a plug tap.

I am doing a deep tap of approx 3/4" depth in what is suppose to be 1018. I am using plenty of oil and keeping a straight pressure on the tap. I am only turning a 1/3 to 1/2 turn on the tap before backing up to clear the burrs and reoiling and then another 1/3 to 1/2 turn, and repeat.

The funny part of this is the first side I did I only broke one tap and I think I let that one get a sideways pressure causing it to break. I ordered this metal from a company and it cut to length to speed up the construction of my grinder. They supply flat bar in 1018 and A-36. I suspect that this may be a piece of A-36 that was sent by accident or deliberately to finish out an order. I am getting maybe 1/4” + or – into the metal before I usually snap a tap.

Ok now you have all the same info that I have on this subject I am looking for suggestions here!! I am determined to finish this project as I originally started it. I only have about 8 more holes to tap! If I don’t go broke buying taps that is!!!!

Am I using the wrong style of tap for deep treading?

Is a titanium tap superior to the plain steel tap?

What do I do to minimize breaking the taps that I not already doing?

Any suggestions or help would be greatly appreciated, maybe some of the machinists we have on this site would care to comment!!!!!!!!!!!!!!!!!

 

[balibalistic]

Try drilling slightly oversize, start hole with a sprial tap and finish with the plug if its a bling hole.

 

[12345678910]

Stop doing it wrong

Firstly Lowes is a general hardware store and is likely selling ok quality stuff, but an industrial machinery and tooling supplier will sell better quality taps at lower prices with knowledgeable staff and a large selection.

Sure I would go up to the 1/4"-20 thread that most people are using. It's much more common and likely cheaper to find tooling and fasteners.

As I see it though the biggest problem is that:
You are using a "Plug" tap to start a hole and it can't handle that.
If you do the same thing in a larger diameter, you will have the same problem.

In hand taps there are three grades to be used in the order
1. taper
2. plug
3. bottoming

This is a random link that shows photos of all 3 types.
The taper tap is "pointier" and cuts gradually into the hole.

http://www.victornet.com/subdepartments/HS-Hand-Taps-NC-and-NF/1250.html

The Plug and Bottoming have gradually flatter points to get as close to a full thread as possible on a blind bottom hole.
On a through hole, you may just use the taper tap if it is long enough to go all the way through, but you cannot get away with skipping straight to the plug.


There are also taps made for machine use that have helical flutes.
Spiral point and spiral flute

Although they cost more, I prefer spiral point as they have less tendency to twist off than a hand tap does.


Another consideration is:
What size drill are you using?

a 10-24 thread at:

74% is a #26 drill .147
you could even go down to about 50% thread by going up to a larger drill by a # size or two
(find a tap drill chart online, I can't do the calculation in my head)


Starting Straight:
It is easy to break off a tap with sideways pressure, or not starting a tap straight.

Put your tap in a drill press chuck, remove the belt and turn the tap by hand for the first several turns until it starts straight.

 

[Nathan the Machinist]

The above advice is so spot-on that I have very little to add.

I like Moly-Dee tapping fluid. It is the best I have tried.

I will reiterate the need to keep things aligned and use a tapered tap if it is a thru hole.


edit: If you have really "dirty" steel (like "hey - there's a chunk out of a 64 Buick bumper stuck in there") you're going to have a tough go of it.

 

[drewfacehotm]

another trick to keep the tap straight if you have the part clamped to your drill press table, right after you drill the hole unchuck your drill bit and put a center drill or a small chucking center in the chuck, that way with one hand you can press the point into the tap handle with the drill press and the other can tap the hole and the center will keep your tap straight.

 

[Nathan the Machinist]

another trick to keep the tap straight if you have the part clamped to your drill press table, right after you drill the hole unchuck your drill bit and put a center drill or a small chucking center in the chuck, that way with one hand you can press the point into the tap handle with the drill press and the other can tap the hole and the center will keep your tap straight.

Hell, I'll chuck up the tap and run it in under power. Small taps (this is almost a small tap) like speed and a continuous run. This is not a recommended way to do it - but it works for me. Doesn't hurt that my "drill press" has a spindle break. Reduces sphincter puckering.

...haven't broken a tap in years...

 

[Dixieblade57]

Thanks to everyone who responded! I figured I might me using the wrong tap.
I agree probably should habe went to a larger size, in fact I already had said that.
I have already taped 24 holes like this as I am building a sliding rest on this grinder like this one in this post.
http://www.bladeforums.com/forums/showthread.php?t=466024

So will order some more taps and try to finish it out.

Which is better a titanium coated tap or just a high carbon steel tap?

 

[Nathan the Machinist]

Which is better a titanium coated tap or just a high carbon steel tap?

Neither. Most good taps are HSS. For whatever reason, despite the fact they're not used at high speed - the HSS holds up better.

 

[drewfacehotm]

Hell, I'll chuck up the tap and run it in under power. Small taps (this is almost a small tap) like speed and a continuous run. This is not a recommended way to do it - but it works for me. Doesn't hurt that my "drill press" has a spindle break. Reduces sphincter puvckering.

...haven't broken a tap in years...

i've broken more taps hand tapping than machine tapping lol. tapping attachments are fun too, just pull up and it reverses out, thats the best.