re:Final leadscrew design - thanks to all (not yet?!?!)

Ron wrote:

>I've uploaded a Final Design file detailing, what else, but the
>final design.

Ron,

We're not done yet! The drawing you posted will not work!

I think the line snipped (from your paragraph) below may provide a
clue to the problems you are having with this. The bearings ARE
SUPPOSED TO carry the thrust loads. As drawn, the shaft will not
rotate.

To make the current drawing work:

1)Add a retention plate to the leadscrew side(left)of the mount block
OR...
go back to the body used in stackup3.gif (through hole for leadscrew,
bore for bearing OD.)

2)Reduce the size(diameter) of the nut on the leadscrew so that it
only presses against the INNER race of the bearing.

3)Increase the hole size through the retaining plate, so that it only
bears against the OUTER race of the BEARING.

I'm going to repeat the "talk-through" of my earlier post. Pretend
you are making this "fixed style" mount as you read. To avoid
confusion, I will leave out the description of any mounting holes for
the finished assembly. I am also going to "assume" that a 1.25
bearing will fit in a 1.25 bore.(In other words, std.clearances will
be ASSUMED)

Let's also assume:
.500 leadscrew.
Bearings .375 ID, 1.25 OD, .3937 thick
mount block is 1.00 thick

1. Drill a .625 hole through the mount block.

2. Bore (on the same center)1.25 diameter,.780 deep. (the bearings
are .393 each, so when the two are stacked and put in the hole they
will stick out .006).

3. Make a retaining plate of .250 thick stock(it will be somewhere
around 1.5 square). Drill a 1.00 hole through the center of this
plate. Drill 4 holes (near the corners) for the screws which will
hold this retaining plate to the mount block.

4. Drill and tap "matching" holes in the mount block for the
retaining plate screws. (10-32 would be a likely size, based on our
assumptions)

5. Turn the leadscrew end to .375 dia. for two inches.
6. Reduce the last 7/8 of the screw further to .312.

7. Thread (3/8-24) for .375 along the 3/8 diameter.(nearest the end
of the shaft)

Now we have a leadscrew with .750 long at 3/8 diameter(for the
bearings)and some 3/8-24 threads for the locking nut(s). 7/8 of the
end is reduced to .312 for a pulley or gear to drive it.

We also have a mount block with a 1.250 bore (for the bearings),.780
deep. And it has a 5/8 through hole so the leadscrew can easily pass.
There are 4 tapped holes around the bore for the screws which will
hold the retaining plate in place.

There is a retaining plate with a 1.00 hole through the center and 4
smaller holes for the screws which hold it to the mount block.

NOW...

Lets get a couple of 3/8-24 jam nuts and put this thing together.

Place the bearings onto the shaft and fasten with a 3/8-24 jam nut.
(this nut must be able to freely turn within a 1.00 inch hole or the
retaining plate will not fit!) Place a second jam nut against the
first and "lock" them together.

Place the long end of the leadscrew through the 5/8 hole in the mount
block (working from the 1.25 bore side). Continue until the bearings
are seated in the bored hole(they will stick out slightly).

Now place the retaining plate over the short end of the shaft and
tighten the 4 screws which hold it in place and which "lock" the
bearings into the mount block.

If the bearings are "face ground angular contact matched pair",
you're done!

If you are using the plain radial bearings to save money, you have
another step. measure the "end play" in the shaft(while the mount is
assembled) disassemble, and put this "discovered" thickness of "shim"
washers between the bearings. If you have worked carefully, you now
have a fixed mount with a thrust capacity equal to ONE bearings
RADIAL capacity.(see previous posts)

Hope this clears this up.

Ballendo

P.S. Ron,Remember, bearings in contact are a FIXED mount, Bearings
spaced apart are RIGID.

'******************************************************************

>This one is easily <snip> thrust load, clampup is achieved without
>applying thrust loads to the bearings,
>Ron