What tap speed on a milling machine?

[Chris DentonParticipant @chrisdenton53037]

Hi, wondering what speed to run thread taps on a milling machine M4 – M12

Thanks.

[Chris DentonParticipant @chrisdenton53037]

[Roy MParticipant @roym]

Info required:- what material are you cutting? What cutting fluid do you have? What type of tap do you have? Is it a blind hole? What type of machine do you have, ( especially how much control do you have?). There will be a difference in speeds between 4 & 12 mm taps, but the machine power may also play a part in your choice of speed. Roy M.

[paul 1950Participant @paul1950]

look somewhere like here

http://tapmatic.com/images/pdf/BetterCNC%20TappingBroP4-6.pdf

[Chris DentonParticipant @chrisdenton53037]

Basically I'm putting new pulleys on the milling machine and wondering what size to use.

It's a 1410rom motor with VFD. So I'm wondering what the lowest spindle speed I'd need would be!

Thanks.

[Enough!Participant @enough]

I do this on the lathe using a VFD-driven motor and the speed control lets me drop right down to zero. I start there and increase speed until the tap is cutting and at a speed that I don't feel is going to run away with me. In any event, the speed might be classified as dead slow.

I don't use this method at all for blind holes and frankly, at these speeds consideration of materials and cutting conditions are largely academic.

I would try to arrange the VFD setup to allow you to run down to zero speed (in can be handy in other situations too) but If you really need a bottom number, work out from the tap-pitch vs speed how long it will take for a tap to run all the way down and pick a minimum time that you think you can handle.

(All of the above assumes you are not using a tapping head, since you didn't say – if you are, then the manufacturer's recommendation should tell you what you need to know).

Edited By Bandersnatch on 25/04/2015 15:42:25

[Clive FosterParticipant @clivefoster55965]

Chris

Probably around 90 rpm for M12 in one of the more unfriendly varieties of austenitic stainless steels is about as low as you'd ever need to go judging by the table of materials and speeds in the Pollard Tapping Head manual. Actually most of the speed ranges given are scary high. M6 in up to 0.4% carbon steel at 700 to 1050 rpm! Yikes! Not with my taps it don't. Not even with Mr Pollards recommended tapping head doing the driving. (Despite doing very little power tapping I have a full set of E-Bay bargain Pollard heads. Sad or wot!).

PM me with your E-Mail address if you'd like a PDF of the Pollard list.

However I find 100 to 200 rpm is fine for pretty much everything in both the Bridgeport mill and Pollard 15AY drill. Different speeds may be more appropriate with other machinery. Threads are produced at a rate much more commensurate with my 60 year old nerves than when attempting to use proper speeds. Still far, far faster and more accurate than by hand. Book speeds are probably only useable if you have a proper reversing tapping head and depth stops so that the drive is dropped rapidly and consistently once the thread is deep enough.

I also have a much smaller and simpler tapping head with fixed drive on a spring loaded sleeve with about 1/4" of travel. In operation you need to keep the sensitive down feed on drill or mill pretty much in sync with the tap as it winds down into the job. The spring loaded sleeve gives enough error room to make it pretty easy. Need to stop the machine once depth is reached and wind back either by hand or in reverse. Best to have a foot stop switch or good brain- knee co-ordination for stop button operation if using a Bridgeport with the common UK control box location. Bottom speed of 102 rpm on the 15AY drill is faster than I like. 50 to 70 rpm on the Bridgeport is more comfortable. Obviously everything has to be done by eye. Depth stops are just an excuse to break taps! That said I find the simple head quite acceptable in use for jobs where the proper Pollard heads are too large.

Clive.

[Anonymous]

I do a lot of power tapping; if nothing else it is much quicker than doing it by hand. I only use spiral point or spiral flute taps under power, although there is no reason hand taps couldn't be used, albeit not much use for blind holes. For example on the manual mill I'd tap M12 in steel at ~200rpm, M6 at 600rpm and M6 in aluminium at 800rpm. For 8BA in brass I was running at 1000rpm. That is with a Tapmatic or Edelmatic head, depending on tap size. On the CNC mill with a tension/compression head I normally run at a few hundred rpm. On the repetition lathe anything from 1000rpm for M3 in aluminium to 500rpm for 1/4" and 5/16" BSF in steel.

I guess the lowest speed required will be determined by whether you are using a proper tapping unit or simply relying on manually controlling spindle direction. Another factor to consider is that driving larger taps requires considerable torque, so simply slowing the spindle by turning down the frequency on a VFD may not cut it.

Andrew

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