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Threading by hand
wongster:
I've finally completed the boring job.... Some pics attached. I was so carried away with it that the bore is almost straight through without the step to hold the die. The final result turns out to be ok except the hole is a little bigger than the die. Difference in size is less than .5mm. Hopefully a couple of set screws will hold it right. The interior of the hole looks bad. As I was creeping up to the final size, the cutter suddenly took a deeper cut than the usual .05mm I set. The smooth finish was destroyed in an instance. Some sand papers were used (from coarse to fine) to touch up the error. The workpiece must have moved out of position to cause this.
As I've no success so far in parting off on the lathe, I think I'll likely to turn down the other end from 40mm to maybe 9mm to fit in my 3/8 jacob chuck. If this is not advisable, I'll cut off the back portion using my vertical bandsaw. This may be tricky as my V-blocks can take only max of 25mm. Any advice on what I should do?
Regards,
Wong
Reckless_Engineer:
Looks like it should do the job and certainly looks the part:thumbup: Grub screws will take up theslack fit of the die and also allow you to adjust the die.
The last cut sounds as if you had push off from the boring bar over the previous cuts and then it bit in on your last cut taking it over size. Next time take a second cut of the same dia. on your 2nd to last cut.
Also is there any reason you held it with the jaws that way around?? You have got alot of material hanging out of the chuck(another cause of the vibration) and the jaws would of been better the other way arond.
Lew_Merrick_PE:
--- Quote from: lordedmond on June 17, 2010, 09:11:39 AM ---Why not screw cut it in the lathe , good practice for future work . finish with a die if you want
then it will be square and the correct tightness
--- End quote ---
Edmond (and All),
If you go to http://www.scribd.com/Lew%20Merrick, you will find a bunch of documents there. One of them is UN Thread Data Chart. This contains a lot of information on (inch-based) UN threads that may be useful to you. One of the columns of information is the threading tool clearance diameter for turning external threads.
The reason I have not done this for metric threads is that there are still five different sets of tolerances and allowances in force for them. Thus, in order to provide a thorough chart for screw and nut pull-out strengths and equivalent pin diameters, I would have to have 15 entries for each major diameter and pitch class of fit combination. The ISO metric screwthread specifications are a mess.
wongster:
--- Quote from: Reckless_Engineer on June 19, 2010, 11:19:05 AM ---The last cut sounds as if you had push off from the boring bar over the previous cuts and then it bit in on your last cut taking it over size. Next time take a second cut of the same dia. on your 2nd to last cut.
Also is there any reason you held it with the jaws that way around?? You have got alot of material hanging out of the chuck(another cause of the vibration) and the jaws would of been better the other way arond.
--- End quote ---
Hello Mr Reckless (hope you're not too reckless like me :D),
Thanks for your reply.
Can you explain a little more on the part "... push off from the boring bar..."? I don't quite understand being rather new to this.
The max I could hold in the Sherline 4 jaw is 38mm. I was hoping that the additional 2mm from my round alu stock can fit but it hit the bed... :scratch: From Sherline's instruction manual, I need to "flip" the jaws around for bigger pieces up to max of 70mm. I should have turned the rod down to 38mm to be within specs but I was worried that I would have enough left to bore. Would 4.7mm wall be strong enough for the die holder? If it is, I'll do up another piece.
Thanks again for your input.
Regards,
Wong
Reckless_Engineer:
I see why you had them that way around now lol :doh:
What you have is fine theres no point re-doing it the other way around.
When boring the boring bar has an habbiot of wanting to push off and flex away from the metal instead of cutting it! Hence the reason for using the biggest bar you can fit in the bore. If you put on a thou cut it may not cut at all, then another thou again not cut. It may do this lets say 4 times you measure again seeing a thou needs to come out so you put another thou on and now the bar doesnt push off and takes the thou and the previous 4 thous that didnt cut taking 5 thou off leaving you 4 thou over sized.
Im not the best person in the world at explaining things im sure someone will correct me if i have wrote something wrong but at least you get the idea.
Oh and on the reckless part, I know more than enough to class myself as Dangerous :zap:
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