Thread: Tapping problem on lathe.

well like the title said it we are having problem tapping on ours new cnc bed lathe. we are trying to tap 3/8-16 in SS304 using coolant. the sell rep send us a special tap (spiral point) that is supose to be a charm in SS but after 3 hole all the thread came right off the part with the tap all melt in it. the coolant we are using is cimcool that is supose to be at around 6 to 9% mix. we put it up to 15% so we have a better lub for ours tap without any succes. we have 100 part to do and dont feel like opening the door (stoping the spindle and everything) to put butterfeild oil on the tap every single time we want to find a way to do it for the futur too.

if any of you got any idea let me know would be realy appreciate.

Sébastien

I found out the main reason why taps fail on lathe (in my case) is if they are not in line with the hole.
IE: you spot and drill a hole, either one of those deviated in the start of the hole or somewhere along the way.

Suggestions: use floating tap holder: this will allow for some play in the tap.
Use (sh*t forgot the name of the tap) regular taps no helical flute or anything- helical flute taps are braking too easy if not in line with the hole. Also a 3-4 flute is the way to go.
And try using peck: this should clear the chips, and give tap a chance to straighten out.

I used to tap alot of 10-32 1" deep holes in 304.
Good luck. That stuff is a bitch.

we have a floating tap holder so tap can move a little bit if the hole deviate. we are tapping 1.500 inch deep to have at least 7/8 of good thread for the bolt.

i mostly think its a coolant problem and not a tool one we are using spiral flute tap 3 flute one

That is kind of deep to take in one shot with 304, try peck tapping in 3 passes.

we have a conversational board fagor 8055 I/TC so you mean doing it in 3 pass like .500 than exit than 1.000 than exit then 1.500 ?

304 doesn't like to be tapped.

Roll Form tap is prolly best for 304.

Maybe some "EP" addititive in a soluable oil coolant would help, but I don't expect you to change coolant just for 100 pcs, so go with the form tap.


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Sweating to the Oldies!
Ox

i read alot on forming tap and everyone seems to say that you need to run on oil to make a good finish and not on coolant like we do. this is why we went for the spiral point tap. i was wondering if i raise the % over 25% if it might help or not.

My thoughts would be a form tap and get your Machininst hand book out and find the drill hole size and go up to higher limit on it. Hole sizes on a tapping chart are your basic in the middle hole size. Peck tapping works good too and the form tap does not make chips to clog or bind anything up.

304 is easy stuff to work.
Nowhere do you mention speed,what speed are you running at and what make of tap is it?

My 2 cents.

Tapping on a lathe kind of sucks. Even if your lathe is nuts, centered, squared, there are still so many bits and pieces(collets and crap) that perfect alignment
is tough. That is the first place I would be checking.

Personally, what I like to do when I need to tap something in the lathe, I do it on the mill. Set my part up so that the tapped hole is on the backside op,
and then second op it in a 3 jaw or pocketed soft jaws on the mill.

I'd also say, already been said, you're going to have to peck it. And do you have clearance in the bottom of the hole for chips???

As a thought, if your drill isn't pretty damn close to perfectly square and centered, you may be rubbing and hardening your hole.
Also if your drill is not perfect, you might not have a straight hole, I've run into that problem.

Originally Posted by Krovvax

we have a conversational board fagor 8055 I/TC so you mean doing it in 3 pass like .500 than exit than 1.000 than exit then 1.500 ?

Exactly, do that and try about 500 rpms or less. You only have a 100 parts, might as well just make do with what you have, worry about speed if the job repeats.

Originally Posted by Dualkit

Exactly, do that and try about 500 rpms or less. You only have a 100 parts, might as well just make do with what you have, worry about speed if the job repeats.

we are using a spiral point tap that seems to realy not like to break the chip when we get out of th hole so im scare that doing it 3 time will kill the tip of the tap faster. we have check all of the tool to be sure they are perfectly center with the chuck. we use a spot drill first than a 135° split point drill made for SS and finally go with the spiral point tap. we run the tap at 200 rpm like the sell rep told us to do with it. what i think is the problem is the hole that got drill 2.000 deep and we tap it all the way to 1.500 deep so i think the chip is getting in the way with the tap since there is not alots of clearance to get out of the way. that way when we get it into reverse the chip squeeze into the flute and melt of simply break the tap teeth. we have spend 4 tap doing 50 piece thats too much we have top fiund a way to get it down to 1 max 2 tap for a 100 part run. learning is expensive loll

If you are tapping deeper than the threads on the tap you will struggle as on reversal the chip will go under the heel of the tap.If that`s the case that`s why the rep has recommended 200rpm but it`s slow,Dualcuts 500 rpm is a lot better.
Did you not say earlier you were using a spiral flute tap but now you are saying spiral point?
Which is it and who makes the taps?

yeah i said spiral flute but that was a mistake we use a spiral point (the one that push the chip trought the hole) and its from dormer. we dont have alot of rep like you guys down there in Quebec canada. so many people are saying i would be better with a forming tap but would that work with coolant since we dont run on oil and i saw at alot of place that forming tap with coolant was a PITA to get good result?

Using a spiral point in a blind hole doesn`t work.When you stop the tap the cuttings coming of the job are still attached and when you reverse the tap it climbs over the cutting and chips the tap.
Get a spiral flute tap,but don`t machine tap deeper than the threads on the tap.For 100 just finish by hand if you can`t get the full depth.