Ok, I'm designing another machine. This is for making
accurate, repeatable cuts on / into large wood beams,
therefore posted to both groups...

I need to build a telescoping vertical elevation section,
much like some Radial Arm Saws have. I want to use standard
steel-supplier square tubing, like 4 to 5 inches, probably
..125 wall or, so. There will be a threaded rod actuator,
possibly based on a trailer jack.

This is a one-off at this point, although I'd like to be
able to document how to make one. IF it works well. So I need
easy-to-get parts. The question:

** What is a good approach to providing bearings for a
sliding, telescoping mechanism with square steel tubing??**

I don't THINK I need antifriction (ball or roller) bearings.
There won't be high-speed or continuous motion.

So, I see something like this:

Two sizes of square steel tubing about 5 inches or so
that telescope with a clearance of, um, .25 inches to .5 inches.
The wall of the outer tube has cutouts of some size and
shape which hold 'things' that reach through and 'bear'
against the inner tube. There probably need to be 'lots'
of these, say 2 per side x 4 = 8 at each 'level' of
contact. Maybe there are only two levels of contact.

What are your thoughts? What is used in existing commercial
designs?

My only thought so far is nylon (other plastic?) bolts in
threaded holes in the outer tube, hex heads inside, jamb
nut on the outside. Adjust for just a little clearance.

Any suggestions or pointers appreciated.
--
Regards, Terry King ...In The Woods In Vermont

The one who Dies With The Most Parts LOSES!! What do you need?

Consider two pieces of square steel tubing, one 5", one 4",
both 1/4" wall thickness (these are hypothetical, not real).
If you put the 4" piece inside the 5" piece it will have 1/2"
clearance, or 1/4" on each side.

What if you welded 1/4" flat bar just inside the end of the 5"
piece, all around? Then the 4" piece would fit it closely. If
there were negative clearance and you did a little grinding,
you could soon achieve a good fit. Call this end (the end of
the 5" piece with the flat bar welded inside it) the "outer
end".

Now what if you welded 1/4" flat bar all around the outside
of the other end of the 4" piece, and similarly ground it to
fit? Suppose the 4" piece fit entirely inside the 5" piece
except for a small bit.

This is the principle of how the telescoping boom on my knuckle
boom truck works. The inner piece cannot exit the outer piece
because the 2 weldments interfere. On my boom, the inner piece
cannot exit the outer piece backwards either, because there is
a pin over the opening.

Grant Erwin
Kirkland, Washington

Terry King wrote:
Ok, I'm designing another machine. This is for making
accurate, repeatable cuts on / into large wood beams,
therefore posted to both groups...

I need to build a telescoping vertical elevation section,
much like some Radial Arm Saws have. I want to use standard
steel-supplier square tubing, like 4 to 5 inches, probably
.125 wall or, so. There will be a threaded rod actuator,
possibly based on a trailer jack.

This is a one-off at this point, although I'd like to be
able to document how to make one. IF it works well. So I need
easy-to-get parts. The question:

** What is a good approach to providing bearings for a
sliding, telescoping mechanism with square steel tubing??**

I don't THINK I need antifriction (ball or roller) bearings.
There won't be high-speed or continuous motion.

So, I see something like this:

Two sizes of square steel tubing about 5 inches or so
that telescope with a clearance of, um, .25 inches to .5 inches.
The wall of the outer tube has cutouts of some size and
shape which hold 'things' that reach through and 'bear'
against the inner tube. There probably need to be 'lots'
of these, say 2 per side x 4 = 8 at each 'level' of
contact. Maybe there are only two levels of contact.

What are your thoughts? What is used in existing commercial
designs?

My only thought so far is nylon (other plastic?) bolts in
threaded holes in the outer tube, hex heads inside, jamb
nut on the outside. Adjust for just a little clearance.

Any suggestions or pointers appreciated.

Terry King wrote:

Ok, I'm designing another machine. This is for making
accurate, repeatable cuts on / into large wood beams,
therefore posted to both groups...

I need to build a telescoping vertical elevation section,
much like some Radial Arm Saws have. I want to use standard
steel-supplier square tubing, like 4 to 5 inches, probably
.125 wall or, so. There will be a threaded rod actuator,
possibly based on a trailer jack.

This is a one-off at this point, although I'd like to be
able to document how to make one. IF it works well. So I need
easy-to-get parts. The question:

** What is a good approach to providing bearings for a
sliding, telescoping mechanism with square steel tubing??**

I don't THINK I need antifriction (ball or roller) bearings.
There won't be high-speed or continuous motion.

So, I see something like this:

Two sizes of square steel tubing about 5 inches or so
that telescope with a clearance of, um, .25 inches to .5 inches.
The wall of the outer tube has cutouts of some size and
shape which hold 'things' that reach through and 'bear'
against the inner tube. There probably need to be 'lots'
of these, say 2 per side x 4 = 8 at each 'level' of
contact. Maybe there are only two levels of contact.

What are your thoughts? What is used in existing commercial
designs?

My only thought so far is nylon (other plastic?) bolts in
threaded holes in the outer tube, hex heads inside, jamb
nut on the outside. Adjust for just a little clearance.

Any suggestions or pointers appreciated.
--
Regards, Terry King ...In The Woods In Vermont

The one who Dies With The Most Parts LOSES!! What do you need?

YOu want it cheap. wrap a piece of waxed paper around the inside tube
and pour the gap with epoxy compound. Use a couple layers of paper to
get the clearances you need. Use a piece of styrofoam to hold it in
place and for the bottom dam on the tubes. For the same process in
bigger dollars use Moglice.

John

Consider two pieces of square steel tubing, one 5", one 4",
both 1/4" wall thickness (these are hypothetical, not real).
...snip
This is the principle of how the telescoping boom on my knuckle
boom truck works.
Grant Erwin
Grant, That's an interesting idea; I wondered how those booms
were spaced internally.

How / what lubrication is used on those booms??

--
Regards, Terry King ...In The Woods In Vermont

The one who Dies With The Most Parts LOSES!! What do you need?

YOu want it cheap. wrap a piece of waxed paper around the inside tube
and pour the gap with epoxy compound. Use a couple layers of paper to
get the clearances you need. Use a piece of styrofoam to hold it in
place and for the bottom dam on the tubes. For the same process in
bigger dollars use Moglice.
I like that idea, too! I do a lot of boat stuff with West Epoxy...

What IS Moglice??

--
Regards, Terry King ...In The Woods In Vermont

The one who Dies With The Most Parts LOSES!! What do you need?

I have seen some pretty slick arrangements using small 6000 series ball
bearings on bolts. The tubing in the one case sat corners vertical and four
bolts with bearings supported the tube running horizontally. The bolts were
set at 45 degrees so that the bearings ran on the sides of the tube.
For your vertical arrangement you would need eight bearings to
completely capture the tube post. Sealed bearings that fit on a half inch
bolt don't run much more than five dollars Canadian from a bearing house.
You might get them as cheap as a couple of dollars each.
Randy
"Terry King" wrote in message
.. .
Ok, I'm designing another machine. This is for making
accurate, repeatable cuts on / into large wood beams,
therefore posted to both groups...

I need to build a telescoping vertical elevation section,
much like some Radial Arm Saws have. I want to use standard
steel-supplier square tubing, like 4 to 5 inches, probably
..125 wall or, so. There will be a threaded rod actuator,
possibly based on a trailer jack.

This is a one-off at this point, although I'd like to be
able to document how to make one. IF it works well. So I need
easy-to-get parts. The question:

** What is a good approach to providing bearings for a
sliding, telescoping mechanism with square steel tubing??**

I don't THINK I need antifriction (ball or roller) bearings.
There won't be high-speed or continuous motion.

So, I see something like this:

Two sizes of square steel tubing about 5 inches or so
that telescope with a clearance of, um, .25 inches to .5 inches.
The wall of the outer tube has cutouts of some size and
shape which hold 'things' that reach through and 'bear'
against the inner tube. There probably need to be 'lots'
of these, say 2 per side x 4 = 8 at each 'level' of
contact. Maybe there are only two levels of contact.

What are your thoughts? What is used in existing commercial
designs?

My only thought so far is nylon (other plastic?) bolts in
threaded holes in the outer tube, hex heads inside, jamb
nut on the outside. Adjust for just a little clearance.

Any suggestions or pointers appreciated.
--
Regards, Terry King ...In The Woods In Vermont

The one who Dies With The Most Parts LOSES!! What do you need?

The lower edge runs on a wheel - that part gets complicated,
actually. But they have big hydraulic cylinders extending and
retracting them, so even if they are a little sticky, it
doesn't mean much. - GWE

Terry King wrote:
Consider two pieces of square steel tubing, one 5", one 4",
both 1/4" wall thickness (these are hypothetical, not real).

..snip

This is the principle of how the telescoping boom on my knuckle
boom truck works.
Grant Erwin

Grant, That's an interesting idea; I wondered how those booms
were spaced internally.

How / what lubrication is used on those booms??

Terry King wrote in message ...
Ok, I'm designing another machine. This is for making
accurate, repeatable cuts on / into large wood beams,
therefore posted to both groups...

I need to build a telescoping vertical elevation section,
much like some Radial Arm Saws have. I want to use standard
steel-supplier square tubing, like 4 to 5 inches, probably
.125 wall or, so. There will be a threaded rod actuator,
possibly based on a trailer jack.

This is a one-off at this point, although I'd like to be
able to document how to make one. IF it works well. So I need
easy-to-get parts. The question:

** What is a good approach to providing bearings for a
sliding, telescoping mechanism with square steel tubing??**

I don't THINK I need antifriction (ball or roller) bearings.
There won't be high-speed or continuous motion.

So, I see something like this:

Two sizes of square steel tubing about 5 inches or so
that telescope with a clearance of, um, .25 inches to .5 inches.
The wall of the outer tube has cutouts of some size and
shape which hold 'things' that reach through and 'bear'
against the inner tube. There probably need to be 'lots'
of these, say 2 per side x 4 = 8 at each 'level' of
contact. Maybe there are only two levels of contact.

What are your thoughts? What is used in existing commercial
designs?

My only thought so far is nylon (other plastic?) bolts in
threaded holes in the outer tube, hex heads inside, jamb
nut on the outside. Adjust for just a little clearance.

Any suggestions or pointers appreciated.

Tell your metal supplier that you want "Telescopic Tubing". It may
cast a little more but it will save you a load of work. -Steve

UHMW would work well for bearing material. Look here
http://woodworker.com/cgi-bin/FULLPR...ARTNUM=813-784

Frank

"Terry King" wrote in message
.. .
Ok, I'm designing another machine. This is for making
accurate, repeatable cuts on / into large wood beams,
therefore posted to both groups...

I need to build a telescoping vertical elevation section,
much like some Radial Arm Saws have. I want to use standard
steel-supplier square tubing, like 4 to 5 inches, probably
.125 wall or, so. There will be a threaded rod actuator,
possibly based on a trailer jack.

This is a one-off at this point, although I'd like to be
able to document how to make one. IF it works well. So I need
easy-to-get parts. The question:

** What is a good approach to providing bearings for a
sliding, telescoping mechanism with square steel tubing??**

I don't THINK I need antifriction (ball or roller) bearings.
There won't be high-speed or continuous motion.

So, I see something like this:

Two sizes of square steel tubing about 5 inches or so
that telescope with a clearance of, um, .25 inches to .5 inches.
The wall of the outer tube has cutouts of some size and
shape which hold 'things' that reach through and 'bear'
against the inner tube. There probably need to be 'lots'
of these, say 2 per side x 4 = 8 at each 'level' of
contact. Maybe there are only two levels of contact.

What are your thoughts? What is used in existing commercial
designs?

My only thought so far is nylon (other plastic?) bolts in
threaded holes in the outer tube, hex heads inside, jamb
nut on the outside. Adjust for just a little clearance.

Any suggestions or pointers appreciated.
--
Regards, Terry King ...In The Woods In Vermont

The one who Dies With The Most Parts LOSES!! What do you need?

Terry King wrote:

YOu want it cheap. wrap a piece of waxed paper around the inside tube
and pour the gap with epoxy compound. Use a couple layers of paper to
get the clearances you need. Use a piece of styrofoam to hold it in
place and for the bottom dam on the tubes. For the same process in
bigger dollars use Moglice.
I like that idea, too! I do a lot of boat stuff with West Epoxy...

What IS Moglice??

--
Regards, Terry King ...In The Woods In Vermont

The one who Dies With The Most Parts LOSES!! What do you need?

Moglice is a bearing material used to repair ways in machine tools. You
can get it in either liquid two part or putty two parts composition. It
has wear material in the epoxy compound. The bad part is that it is
expensive but not so if you consider the time it saves in a repair.
Here is the site for more info:

http://www.moglice.com/


John

I have seen some pretty slick arrangements using small 6000 series ball
bearings on bolts. The tubing in the one case sat corners vertical and four
bolts with bearings supported the tube running horizontally
Randy, I'm having trouble visualizing this interesting arrangement.
Can you explain more, or point to any sketch etc???
Thanks!

--
Regards, Terry King ...In The Woods In Vermont

The one who Dies With The Most Parts LOSES!! What do you need?

THANKS! For the many ideas and perspectives.

-- I will check with my supplier about 'telescoping' tubing.

-- The different high-density bearing materials look very
interesting. And some can be 'machined like wood' making
adjustable-clearance approaches more reasonable.

-- I will put a dial indicator inside some 4 inch tubing I
have to see the variation in size over a couple of feet.

What if: UHMW or similar was used as sliding bearing material,
grooved to fit over the 'flash' on one internal side.

What if: that side and another side adjacent to it had
fixed-to-the-outer-tube UHMW, and the other two sides had
large areas of UHMW backed up with, um, 1/8" plate,
with clearance adjustment screws thru
tapped holes on those two adjacent sides. The total raw clearance
would have to be reasonable for all that UHMW and backing plates.

What if: 'almost all' the clearance was adjusted out, pushing the inner
tube 'into the corner' with the two fixed UHMW bearings. I don't need
really low friction: probably 20 pounds would be 'pulling down' and a
strong leadscrew jack pushing up. I could 'antibacklash' like I always
do on my radial arm saw, if necessary.

This is not intended to smoothly move a cutting tool, but rather to
position and reposition the cutting tool which has it's own degree
of freedom for the cut. I need 'woodworking' accuracy here, not machine-
tool accuracy. Maybe say .016 to .032 repeatability of position would be
workable, .005 Would Be Nice.

I would appreciate your comments or suggestions on the above.

OK, this is starting to make more sense. I know some pitfalls I might
have missed. I know some new materials and ideas. I have some stuff to
research more. I hope to get closer to an approach I'll try
Real Soon Now. I'll keep in touch here.

Everyone's suggestions are appreciated.

--
Regards, Terry King ...In The Woods In Vermont

The one who Dies With The Most Parts LOSES!! What do you need?