Bad day of threading

S

Shepherd

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So after mucking around for three hours with getting the right fears, then feed rate, finally started to cut some 5/8-11 tpi threads on my craftex 3 in 1...first pass, nice and light, perfectly lines up with thread gauge, good to go, right?

not so much. Taking very small passes with the compound, set at a little less than 30 degrees of perpendicular, bit square to the piece, the bit seemed to be slicing with its left edge....but after several passes, it just kept chewing up the thread, never getting any depth...

only thing I can think is when dialling the cross slide back to zero, it was not exact each time...I had a stop set up though, so it was pretty close... Here was my routine:

set cross slide to zero
dial compound in .010-.020
Engage half nut on the 4 every time...is it possible I missed by a " notch" engaging this?
dis engage at end relief ccut dial cross slide out
dial cross slide out, return to start


Any and all advice appreciated!
 
Without pictures, it's a bit hard to tell. Could it be that there's not enough relief ground on the side of your cutter?
 
I'd look at the tool bit. It sounds like it might be set above center, or possibly not ground with proper side clearance. Remember, the side clearance must match the lead of the thread or it will drag, so the left side must have more clearance than the right. How about a pic of your set-up?

Tom
 
Cutter was on centre, would have to check the side clearance...I'll get a pic tomorrow night.

one other thought...the gearing was a particular hassle. Machine shows 72-120/127-33, Chinglish manual shows 72-120-33, and the Grizzly manual I have (much better written) shows 72-127-33....would this affect the shape of thread or the cutter picking up the thread on each pass, or just the pitch?
 
I always try to set it the compound to 29[SUP]o[/SUP]. The problem I always have is that the scales on the Hercus have 0 as parallel to the ways, rather than perpendicular. I usually start out messing up the tops of the threads before I catch it. Once I reset the compound to 59[SUP]o[/SUP] (29[SUP]o[/SUP]from perpendicular), it works out properly.
 
Flutedchamber and Tom are correct in having enough side relief. Is you compound set to 29-1/2* ?

Also, what material and what are you using for lube?
 
Shepherd said:
How critical is the angle? So long as its less than 30?
Click to expand...

The idea of having just less than 30* is to rough in the thread using the compound until you're almost at size. The last few thousandths ( just more than a spring cut ) are done with the cross slide to cut a thread that is smooth on both sides.

If zero degrees is parallel to the movement of the cross slide, pivot it 29-1/2* to the right and tighten it down.

Jeff
 
I've never been a fan of the 29 1/2º thing. If the compound is set to roughly 30º, the tool is essentially cutting on one side. When the thread is nearly to depth, the last few thousandths are taken with the cross slide. Once that happens, the tool cuts on both sides anyway and it doesn't matter where the compound was set (within reason). The theory behind setting the compound to 29 1/2º is that the tool will cut mostly on the left side and a very light cut on the right. This reduces the amount of force on the set-up and consequently reduces the possibility of chatter. Where the theory falls short is when the thread is nearly to size. It's a heck of a lot easier to figure out how far to feed the tool in for the final cut with the cross slide than it is with the compound when it's set to 29 1/2º.

Tom
 
I've never cut a thread in my life yet,this is good in one way.Tubalcain has a Youtube on how to setup for cutting threads.While watching some Youtubes there was a guy who use a toolholder that you square w/spindle chuck and the holder had the tringle shape cutter at the 29*.The cutter was already grind to 60*w/three tips,has anyone tried one of these cutters?Sounds like it helps simplifile the process alittle---Kroll
http://www.youtube.com/watch?v=9y0MmvscBzg
 
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