Roll taps are very useful on copper sheet material (which is very abrasive to cutting taps) and is good on any thinnish malleable metal as it compresses the thread theoretically making it stronger by deforming the grain structure rather than slicing it. They are considerably stronger too. Colin

I find the Thead- flow taps a delight to use. In small sizes they feel more solid, and give confidence, they go well in brass, and I'v used them to make some 10 and 7 BA nuts from steel. Ian S C

Tapping size for roll forming metric taps is easy: Just take the average between nominal size and the usual tapping hole diameter. Say for M6: nominal 6 mm, tapping size 5 mm, for a roll tap use 5.5 mm.

Don't know how it works out for other thread forms, but the manufacturere should know!!!

Greetings, Hansrudolf

P.S. they work also very well in free cutting steel

Edited By Versaboss on 29/09/2013 13:04:08

I still can't transfer photos from my album, but I'v put a chart of recomended drill sizes for Sutton Threadflo taps, and recomended threading speeds, "you got to be kidding" 4BA 3500rpm for al cu soft brass, 2730 for die castings, and leaded steel, I did mine by hand. Ian S C

PS

I realize I have committed the all-too-common sin of asking for information which I should perhaps have first looked up myself. The up side is that the many see potentially useful material rather than just the one.

I looked out my single 5/16" 24 UNF thread-forming tap and ran all three methods of determining the correct tap drill size with results varying between 7.3mm and 7.4mm. This might seem quite a large range but there is the variable of thread depth to consider; I used 75% for the Guhring calculator.

I also checked three other possible hardcopy sources:

Machinery's Handbook 1943 – apparently unknown then

Newnes Mechanical Engineer's Pocket Book 1997 – not mentioned

Tubal Cain's Handbook – not mentioned so far as I could see but he was very keen on the correct size for conventional taps

Harold Hall's Data Book (WPS 42) – he calls them fluteless and gives 7.3mm

Now off to the workshop to form a thread with the thought in mind that these taps presumably require a relatively large degree of axial pressure.

Ian S C:

Sorry if I wasn't clear – I did find your table in your photo album. I see you have now been able to transfer the photo to this thread, something I have yet to attempt.

I did, however, produce a thread in softish aluminium without difficulty. As it happens, my Roltap brand tool turned out to be marked with a tap drill size – 7.4mm – and I actually used 7.35 which was my nearest drill and fell neatly between the high and low range figures. Under a lens the thread appeared to be not quite fully formed.

Harold Hall makes some interesting comments including that a good quality lubricant, not a cutting oil, must be used; my favourite Rocol RTD claims to be suitable for "forming operations"

Ductility is the ability of a material to plastically deform before fracture. It's got nothing to do with how soft or tough a material is, or its machining properties. According to the Copper Development Organisation aluminium bronze is ductile, which is why form tapping works.

Regards,

Andrew