A "Dooh" Headslap Moment

[ozzie46]

I broke two 2-56 taps in 2 seperate engine cyl blks then realized I had used a tapping drill size for brass or aluminum. The blks are CAST IRON!! Dooh! :wall: :wall: :wall: :wall: :wall: :wall:


Now I get to make some more blks. Oh well practice makes perfect. ;D ;D

Ron

 

[bearcar1]

"Well you stupid ............ " Oh never mind. Don't you just hate it when that happens? Been there, done that so you are just another name to be added to the growing list of tap breakers and scrap makers. Rof} Too bad there isn't a method of chemically dissolving taps in cast iron like there is for Aluminum and Bronze.

BC1
Jim

 

[rake60]

I have several models with mock bolt heads super glued to cylinder heads.
They cover holes with 2-56 taps broken off in them.
I'll bet you can't tell which ones they are.


Rick

 

[JMI]

I broke two 2-56 taps in 2 seperate engine cyl blks then realized I had used a tapping drill size for brass or aluminum. The blks are CAST IRON!!

I'm unfamiliar with different tap drill sizes for different material ???
Where can I find that info?

Thanks much

Jim

 

[speakerme]

Hello,

This may help you:

http://www.efunda.com/designstandards/screws/tapdrill.cfm

p.s.

The machinists handbook is a good reference, and don't be afraid to Google "drill tap sizes" as I did to get you the reference. For all the materials that I use, I follow the recommended size for the tap or die. Specialty items like stainless have specialty taps and dies, follow the rec. for drill size that comes with them.
Alum., steel, brass, bronze & Plastics, I use the standard charts. Aluminum and some other soft metals do have spiral taps that drill and tap at the same time, (first part drill, 2nd part tap) but take a little getting used to, best used in production work, with fancy and expensive holders.

Print out the above reference if you want and post it on the wall of the shop.

Hope this helps,


Best Wishes,

Chuck M

 

[tel]

I have several models with mock bolt heads super glued to cylinder heads.
They cover holes with 2-56 taps broken off in them.
I'll bet you can't tell which ones they are.


Rick

Rof} Now that you mention it, so 'ave I - but don't tell anybody.

 

[websterz]

I have several models with mock bolt heads super glued to cylinder heads.
They cover holes with 2-56 taps broken off in them.
I'll bet you can't tell which ones they are.


Rick

Duly noted for future use! :bow:

 

[Thad Swarfburn III]

... I had used a tapping drill size for brass or aluminum....

Ah, while this makes perfect sense to me, I have never heard of different charts for different metals! Do I take the usual charts that are posted in every workshop to be for mild steel?

speakerme's efunda link has a chart, but it doesn't specify what metals it's for. Anyone have a link to a chart that lists multiple metals? Or can anyone offer a percentage increase/decrease for different metals?

Thanks,
Matt
(4th year apprentice)

 

[ozzie46]

Try this.

http://littlemachineshop.com/Reference/tapdrill.php


Ron

 

[mklotz]

The relevant parameter is called the depth-of-thread (DOT hereafter), normally expressed as a percentage. The smaller the DOT (i.e., larger tap drill), the easier it is to tap the hole.
DOT is related to tap drill size via the equation:

TD = MD - 0.013*DOT/P

where:

TD = tap drill diameter
MD = thread nominal major diameter
P = pitch expressed in tpi

If you use the DRILL program from my site to find tap drill sizes, it will present you with a list of materials and their recommended DOTs before asking for the DOT you wish to use.

MATERIAL                     % DOT

MILD AND UNTREATED STEELS             60-65
HIGH CARBON STEEL                 50
HIGH SPEED STEEL                 55
STAINLESS STEEL                  50
FREE CUTTING STAINLESS STEEL           60
CAST IRON                     70-75
WROUGHT ALUMINUM                 65
CAST ALUMINUM                   75
WROUGHT COPPER                  60
FREE CUTTING YELLOW BRASS             70
DRAWN BRASS                    65
MANGANESE BRONZE                 55
MONEL METAL                    55-60
NICKEL SILVER (GERMAN SILVER)           50-60
Depth of thread desired [75 %] ?

 

[cobra428]

I had read in the book...Machine Shop Trade Secrets that a general rule of thumb was to pick the next biggest drill that the tap guide recommends. #6-32 tap (drill #36) use a #35.
2.5 thou bigger won't hurt but will ease tapping. It's been working for me!
Tony

 

[Stu Miller]

Ozzie,
Just out of curiosity, are you using hand taps or spiral point taps?

 

[ozzie46]

I'm using hand taps. Since I am now using the proper tapping drill size I have had no further problems so far. I don't tap under power. I do it by hand. Also I machined up a sensitive tapping tool for small taps and am now using the drill/mill spindle to align the taps. Made a world of difference.

Ron

 

[Stu Miller]

Ozzie,

I mostly hand tap and discovered I quit breaking taps when I went to spiral point taps. Even though they are described as machine taps, In my opinion they work much better than hand taps.

 

[cobra428]

We have all been talking about the hole size for tapping but.......one of the biggest (I think) reasons for breaking taps (especially small ones)..... you go off on an angle without one of these!

http://www.use-enco.com/CGI/INSRIT?PARTPG=INSRAR2&PMAKA=318-0007&PMPXNO=953101

There are smaller ones and less $$$. The one above is way to big for this hobby but LMS and HF sells smaller versions.
Tony

 

[Stu Miller]

For a tapper appropriate to small taps, go here.

http://www.frets.com/HomeShopTech/Tooling/MiniHandTapper/minihandtapper.html

I built a knock off of it myself, but my project grew a bit. It will handle taps to #10.

Also, take a look at his other projects. He does some neat tools and tooling.

 

[shred]

Marv and others have posted some nice in-situ tap guides for small taps as well. Very handy sometimes.