Threading drilled holes in PM castings

[tghsmith]

for tapping on a machine I use the same type small drill chuck to hold the tap instead of a tap handle,, you get a better feel of what the tap is doing. It makes you go a little slower.. you'll back out and clean the tap more often.. If you don't overtighten the chuck the tap can slip instead of breaking.. A tap handle just give the urge to power on in untill things go snap.. (so much for saved time)

 

[jbolt]

The chance of me never breaking a tap is zero. After 40+ years of experience I still get impatient when on the bizzilionth and one hole or taping a material I am not familiar with or not sure of the composition. Hand tapping small taps is a bit of an art and just take experience. High quality taps can be worth there weight in gold. For taps under #6 size I use a pin vise vs a t-handle. Less torque and more feel.

Taps often break on back out when too much material is packed into the flute and there is no more room for the break chip. We have all had that "oh crap" moment backing out a tap and it does not want to turn. A spiral point tap cuts at the tip and pushes material forward. That is why they are best for through holes but can be used for starting holes. Spiral flute taps are meant for blind holes and have more room for the chips and will pull the chips out of the hole to some degree. The only thing I find general purpose taps good for is making into bottoming taps.

 

[Eddyde]

Do not use lubricant when tapping cast iron, if you do, it may cause the fine chips to clump together and bind up the tap in the hole.

 

[Kiwi Canuck]

My question is did you get the broken tap out?

I bought a cheaper set of taps and dies in a kit and have been switching out all the smaller ones for better quality ones as I go along.

I've still used some of the taps from the kit on the Mill and have tapped a lot of 5mm threads while mounting the DRO scales.

So far I've been lucky and not had any issues, but did have one bind while backing it up and it got my attention.

I don't believe I've ever broken a tap that was too hard to get out but I've certainly assisted in a few removals of broken taps that have been very tough.

What a sick feeling when you hear that sound.

I've been eyeing these up but have not bought any yet.

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David.

 

[mmcmdl]

Good luck with those extractors .

 

[NortonDommi]

Taps have very finite lifetimes and a buck of old rusty taps will cause you more headaches than they are worth.

I bought a cheaper set of taps and dies in a kit and have been switching out all the smaller ones for better quality ones as I go along.

macardoso[COLOR=rgb(0, 0, 0)] [/COLOR]Made another very salient point about tapping drill sizes, I reckon most breakages are due to too tight a hole size and old worn taps will bind up. I'm like Kiwi Canuck in that sometimes I have no choice but to buy cheap but I try and replace with good quality ASP. I've started working through the most used sizes and have spiral flute for through holes and now pretty much stick with Voelkel serial taps for everything else and hard materials.
Old taps have uses such as cleaning gunk out of holes. Cleaning after glass beading etc, they can also be turned into mini reamers and chisels.

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[ThinWoodsman]

Good luck with those extractors .

No kidding - just one more thing to break off in the hole

I cleared up a few mistakes with a carbide drill like the Omega, but everybody has their favorite method of course.

 

[kb58]

...My question is did you get the broken tap out?..

No. Since it broke while backing it out, it's stuck pretty well, and the last thing I need is a broken extractor. It's one of four holes that mounts the VFD, and at the bottom, so it's not a big deal.

 

[Cobra]

No. Since it broke while backing it out, it's stuck pretty well, and the last thing I need is a broken extractor. It's one of four holes that mounts the VFD, and at the bottom, so it's not a big deal.

Good attitude! If it really mattered you could move over a 1/4" on the bracket and try again but in this case I think you have the correct approach.
Jim

 

[B2]

Maybe PM uses better cast iron than my ENCO and Grizzly machines! That stuff seems to cut like I was tapping a sand castle.

Sand Castle: That is excellet description of my tapping experience on my PM 940M vertical casting. One has of bear down more than normal to get a tap to even start to grab and cut threads.
-- Dave