Re: [Emc-users] Suitability question

[Gene Heskett]

On Saturday 03 September 2016 09:58:45 andy pugh wrote:

> On 3 September 2016 at 03:52, Gene Heskett  
wrote:
> > No common sense west of the big pond...
>
> I have observed that from here :-)
>
> If you are making a thread for your own use you do not need to stick
> to any standard.
> My drawbar is held together by an M14.25 x 0.9 thread. Because that is
> what gave me a 1:1:1 split between the two parts and the thread.
>
> Make an oversize nut that will fit over the shaft.

Which has to fully, and tightly, engage a 50 tpi thread cut in that 
12.7mm shaft beyond the 12m diameter quasi-smooth shaft where the drive 
pulley will sit.  With ATM a drive or press it on fit, my digital 
calipers say it is 12.04mm in diameter. So I'll compose a g76 line for 
the thread, but use a start point a couple mm's off the end of the 
shaft.  If it really chews it up, I'll make the nuts, all 3 of them, one 
with the tapered thread for the screw grabber compression, and then 
decide if I need to turn it on down to 10mm's.  Pulleys and belts yet to 
be ordered.

I bought a 2505 nut mount block which hasn't arrived yet, but need to 
hang the screw up with wires to determine how much of a spacer block I 
need under it to best fit both the tail end bracket to hold its floating 
bearing, and what I have to cobble up and make for the motor mount and 
drive belt, where the qcgb used to be.  The screw is long enough that 
its thrust bearing could be on the inside face of a 1/2" thick alu 
plate, but I suspect I'll have to make spacers to hold the plate out 
from the bed casting, using longer bolts into those holes, in order to 
do that.  That imply's a spacer block under the nut mount to couple the 
nut to the apron or possibly to the now unused apron retainer bolts 
since my new apron is fixed to the front of the saddle with 4 grade 8 
1/4" bolts on each side of the x drive bearing. This has to leave room 
under it for the motor to pass by the screw.  With room for the motor 
mount slider to move and tension the backlash out of the timing belt 
drive. By the time I find the right bellows for the screws swarf 
protection, its likely to get crowded anyway.  This also will get easier 
once the x drive is finished because then I'll know where the z screw 
has to be hung for max bellows clearance all around.  Bellows 
compression room on the right for full travel says the nut will be 
mounted on the left half of the new apron plate. Tiddly stuff, best done 
in the proper order, which means get the saddle back on it, with fresh 
wipers, making a new full length front gib plate, lapped flat on the 
contact face and shimming if needed.  As is turning the rear one over, 
lapping it flat and adjusting its shims. Time killers...

I found, when I built the new Z drive for the toy mill, that I needed 30 
or 40 lbs of tension on that belt else the belt was an easily measured 
source of backlash. I worried about the motors bearing life, but that 
was 6 or 7 years of heavy use since, no complaints yet.  That kevlar 
corded belt has not stretched that I can detect.

But get some coffee on, and see if my lady needs anything.  I'm sitting 
here waiting for the morning pills to kick in, my back was killing me 
when I tried to roll out of bed 45 minutes ago.

Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page 

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Re: [Emc-users] Suitability question

[andy pugh]

On 3 September 2016 at 03:52, Gene Heskett  wrote:
> No common sense west of the big pond...

I have observed that from here :-)

If you are making a thread for your own use you do not need to stick
to any standard.
My drawbar is held together by an M14.25 x 0.9 thread. Because that is
what gave me a 1:1:1 split between the two parts and the thread.

Make an oversize nut that will fit over the shaft.


-- 
atp
"A motorcycle is a bicycle with a pandemonium attachment and is
designed for the especial use of mechanical geniuses, daredevils and
lunatics."
— George Fitch, Atlanta Constitution Newspaper, 1916

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[Emc-users] Suitability question

[Gene Heskett]

Greetings everybody;

Working on the drive shaft for the x screw in this Sheldon.

1. I have 1/2" A2 rod, IOW 12.7m's in diameter.
2. I've already cut 50 tpi threads, both straight and tapered, on the 
inner end. The tapered section will have 6 slots cut into it by EDM, and 
a tapered thread nut will then put the squeeze on the 6 fingers formed 
by the cuts, with the squeeze being the grip on the end of the screw. 
For both thrust and rotational forces.
3. I'd like to use a 12mm bore timing pulley on the outer end, and 
another 50 tpi nut to adjust the load/preload on the roller bearing 
thrust washers I am installing on the OEM crossfeed handle bearing 
screw-in that exists now but with a counterbore in the outside end, 
probably covered with a felt swarf washer. I have taken some pix, but 
they are still in the camera.

But, 50 tpi's thread depth calculations tell me the bottom of the threads 
valley will only be 10.95mm in diameter.  So in order to get the nut to 
the full depth threads behind what should be a fairly smooth 12mm shaft 
to fit the stock 12mm pulley bore, I am going to have to cut a partial 
thread the full length of the shaft just to get the nut to the full 
depth threads.  Obviously I'm not excited about that.

So, should I do that, or go ahead and turn the shaft on down to 10mm's 
and order pulleys accordingly? I have some fresh, green, threadlocker to 
enhance the grip in any event.

And I have to chuckle at the vendor who sold me the 1500mm long 2505 
screw kit.  The end of the screw is 10mm's, and the flexible coupling to 
hook it to a motor?  Its 6mm's on the motor end.  But  my motor has a 
15mm double flatted shaft.  No common sense west of the big pond...  
That too will be belt driven.  And I'm scanning ebays offerings for a 
pair of rubber bellows type boots to cover this screw with.  Just 
haven't found what I think I need yet.

The *667 hall sensors, and a decent motor mount (assembled bass ackwards 
of course) fell out of the mailbox today, so some of it is coming 
together, faster than I can make use of it. But its progress I try to 
tell me.
Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page 

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