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PixMan (05-10-2015)
(05-10-2015, 08:17 AM)PixMan Wrote: I do see one other reason why I like a 5C collet block: The collet "nose" isn't larger than the block.
This feature allows the collet block and workpiece to be held in the middle of the vise jaws where the force won't shift the movable jaw to one side or the other. The ER style has a nut much larger than the collets so you can't as easily get it in the middle of the jaws. A parallel spacer on either side of the hex/square of the block solves that.
The cutter in use is perfect for the application, and looks vaguely familiar.
Thanks Ken - what I didn't capture in the picture is that I had the square collet block sitting on the other side of the vise, so that the jaws were parallel when tightened.
I got that F4042R cutter of a guy I know in central MA, who I met on some obscure corner of the internet. Turned out to be a really nice guy who sold it to me for a ridiculously cheap price. It has sat in my cupboard for far too long and I am really happy to have finally been able to use it and I am really happy with it.
(05-10-2015, 08:26 AM)DaveH Wrote: I won't come undone provided it is tightened correctly (normal force).
To rely on the fictional force between the nut/bolt head and the component to stop the thread coming undone is not the correct way to tighten a thread.
Hex milling - have you tried a smaller cut say .005" to .010" to see if the dimensional difference decreases.
DaveH
Thanks Dave - I ran out of time but I will try some test cuts on some scrap and see if it makes a difference.
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I was just thinking about the difference in drawbars I've used.
On turret mills (Brideports and their clones), all I've ever seen were 7/16-20UNF threads. A finer thread has less helix angle. Would that make it less prone to loosening?
The machines I've used with NMTB 40 and 50 tapers were Cincinnati, Milwaukee, Kearney & Trecker milling machines, beasts as compared to a Bridgeport. The drawbars on those were like Darren's, coarse thread 1/2-13UNC and 5/8-11UNC thread. The other difference was that the drawbars were not directly tightened against a shoulder. Instead, you screwed the drawbar into the holder until it bottomed out, back off by a 1/2 turn and snugged up a check nut under the end hex milled on the drawbar. Yes, you needed two wrenches and three hands to change a tool, and probably why DeVlieg and others developed "quick change" systems.
I wonder if this design had distinctly different characteristics of maintaining tension. Curious.
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(05-10-2015, 08:49 AM)PixMan Wrote: A finer thread has less helix angle. Would that make it less prone to loosening?
Yep
DaveH
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The following 3 users Like Mayhem's post:
EdK (09-06-2015), Highpower (09-06-2015), PixMan (09-06-2015)
OK - finally got some time in the shop and (almost) finished off the drawbars. I decided to reduce the length of the hex. I also had to remove the bearing, as the second one that I purchased had a 13mm bore, where the first had a 12mm bore! So now, only the 12mm race is incorporated into the drawbar and the 13mm race and 13mm bearing are in the quill.
Here they are next to the ones I have been using:
Note the spacer needed to fit between the top of the quill and the pulley bearing housing. This is incorporated into the new drawbar.
Close up (blue is 1/2-13 and red is M12x1.75):
All that is left to do is drive in the ø4mm roll pins and they are ready to put into use
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Both drawbars are now finished and I have almost finished the hammer. I pinned them and then added a chamfer to the hex:
Here you can see the thrust bearing
in situ:
Quill up:
Quill down:
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While I don't have multiple thread designations on my collets and other holders (all are 7/16-20UNF), I really need to cut down the long hex on my drawbar. It's one of those extra long ones made so you can change tools without retracting the quill. What a waste. I have never needed to do that and even if I did the R8 shanks combined with whatever tool is on the "business end" is usually so long that if I didn't retract the quill I'd have to lower the knee.
The shortening will get done the next time I need to tilt the head because I do not have enough ceiling height above the spindle to pull the drawbar out if the head is in the normal orientation.
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Nicely done Darren
I like the thrust bearing - a good bit of engineering
DaveH
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Thanks Dave - I bought the thrust bearing
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RobWilson
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(09-12-2015, 10:03 AM)Mayhem Wrote: Thanks Dave - I bought the thrust bearing
Cheat
Rob
