On 12/26/23 02:35, Linden wrote:
On 2023-12-25 21:56, gene heskett wrote:
On 12/25/23 19:05, Linden via Emc-users wrote:
Hello All,
In the early stages of converting a 13 x 24 inch manual Chinese
lathe to run with Linux CNC.
I have 2 questions regarding replacing the Z axis lead screw with a
3205 ball screw:
What I am thinking is mounting the fixed end in a pillow block at
the head stock end of the lathe and the floating end in a second
pillow block at the tail stock end of the bed. The question I have is
there any reason I shouldn't drive the ball screw from the floating
end? My logic for driving at the floating (tali stock) end is 1 I
have more room for belt reduction at this end and 2 with the fixed
end of the ball screw at the head stock end is that the ball screw
will be in tension when it is pulling the carriage toward the head
stock during cutting and less likely to flex or bend.
The second question I have is what would be a realistic cutting speed
range for the ball screw in RPM? The servo motor I am using has a
top speed of 3000rpm and I am trying to figure out reduction ratio
that is realistic.
Thats a pretty husky screw. I driving from the headstock end with the
thrust bearing at the headstock end of a 25mm by 1450mm screw.
Accuracy wise as long as the thrust bearing mount is dead solid it
should just work.
Another thing because ball screws and swarf don't mix is seal up the
screw areas, so I filled the top of the cross feed and sealed the
bottom of the carriage below the much smaller screw driving the cross
feed. I also bought a pair of bellows that will extend to around
1400mm and made 4 shouldered barbs that plug into the bellows on each
side of the ball nut, and at the bearings, leaving 2 of the the ball
nut bolts out but drilling those two empty holes on thru to allow the
air trapped inside the bellows to blow through the bolt holes when it
is moving rapidly, rapidly in this case might be and end to end of
over 1.3 meters at 120 or more carriage speed.
You pay good money for the screws, protect them.
Thanks in advance for any help or suggestions.
And I hope everybody has a better 2024. And had a merry Christmas.
Cheers, Gene Heskett.
Thanks Gene I had not even considered protection for the ball screws I
think I will need to scrounge up some accordion tube. My 4 year old son
has a plastic one that is about the correct diameter as long as it will
put up with hot chips I might try using it and then get some more.
White hot swarf will burn right thru it. What I got for the long screw
is rubberized wire re-enforced canvas or? I have not damaged it in about
5 years, yet... I do take a stiff bristled paint brush to clean out the
folds occasionally. Put a zerk in the nut I can hit with half a squirt
from a std grease gun yearly. The bolt coupling the crossfeed nut to
the crossfeed is removed to lube that tiny ballnut so it stays
relatively clean & lubed.
The carriage got turned over and the bottom of the screw channel closed
up with a strip of alu rack panel except for the rear, glued in place by
some sort of metal containing rtv, then the crossfeed slider which was
the long version, having removed the taper attachment since linuxcnc can
do that was similarly was sealed up by glueing in another strip of
paneling above the screw. Now the only way in is if the crossfeed in
far enough to expose the screw behind the tool holder pad which replaces
the compound with a similar height of cast irom made from a sprew cut
off a large car wheel hub. We have in this small town a cast iron
facility that makes all the wheels for White Trucks. I went looking for
some scrap to make the pads, got handed a sprew that weighed about 35
lbs & they refused any attempt to pay them. I had fun cutting that up
with a diamond saw.
Take care, stay warm and well.
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, 1940)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
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