1" X 5 Acme tap

I went to a car boot today and one stall had this tap which apparently was from Colchester Lathes. It appears brand new as still fully wax covered. Also has 2/3 rd depth on it so may be part of a set.

I don't have a Colchester but for £5 I thought it was worth getting in case I was doing a favour for someone.

Anyone in need is welcome to pm me? (and if not I have now a good door wedge)

Acme, and square, thread taps are normally made in sets with increasing thread depth. It would be impractical to cut such threads with a single tap. Either the torque required would be too high, or the tap would be impractically long. The taps are often in sets of three, or five for coarse threads. Here's a home made set of three taps for an 8tpi square thread:

Andrew

Oooooooh, so close!

I've just bought a 3' length of 1" X 5 TPI Acme rod to make a new feedscrew for my ancient horizontal mill. I can screwcut the nut but a tap would be nice for finishing

I wonder if you could pop back next week and see if he's got the other two.

Regards

Dave

David & DaveB,

Left-Hand or Right-Hand?

Best Regards,

Swarf, Mostly!

ACME Taps can be very unforgiving in use and are not the be all and end all of creating a good thread. My pal John tells a good story about the folk who made the CVA toolroom lathes found out finding this out when he worked for them many years ago. One of his jobs was single point turning feed nuts on a tuned up P&W Model C. Bright spark new management hire decided that single point turning in small batches as needed was inefficient. Set(s) of high precision ACME taps bought at eye watering price and several months worth of feed nut blanks sent to the shops and done in a single job. Much quicker, great saving of time and money, bright spark new hire looking very good.

Time came to start using them. A few actually fitted as made and some could be re-worked but around 80% went straight to scrap as having excess backlash, threads off centre or out of line et al. Management unimpressed and bright spark new hire looking for new job. I've no idea if there was a certain element of shop manipulation going on to shift an unliked manager before he did some real damage but John reckoned he could single point a better thread faster than using taps. Having seen him re-cut a worn nut to match a replacement, oversize male form, feedscrew for a Churchill Cub lathe with no backlash that I could feel in about 15 minutes flat from being handed the job I'm more than willing to believe him. Especially as he spent more time setting the lathe, a Kerry AG he had rebuilt, up than doing the job.

Sort of thing that really brings home the difference between a real pro and home shop guy. Probably take me an hour to do as well.

Clive

Clive Foster:

In defence of of the home shop guy, the latter gets four times the fun!

The limiting factor seems to be the core size of the nut; I believe GHT managed to cut one as small as 3/8". Can you remember any details of this interesting operation? I imagine that in most cases the tool has the same profile as the thread but I wonder if there might be some advantage in a narrower tool which could cut alternately on leading and trailing flanks.

Yep done with a narrower tool taking shavings off front and rear flanks of the thread in the nut to remove wear and make the grooves wide enough to fit the overwide male section on the new screw.

Clive.