I am using a swing arm for my home made device.
It was inspired by the swing arm lamp like this one
http://www.lightspc.com/img/g-2518.jpg

My swing arm is made of 3/8 square steel tubes and Delrin plates. Tubes are
attached to Delrin plates by 10-32 bolts.
I use steel washers against Delrin. That should give me low friction.

The problem I have is that it's hard to control bolts tightness. If it's not
tight enough the whole swing arm has a significant "play"
If you tight it to much it's hard to move due to high friction.

Is there a good solution for this problem?

BTW: what should I use to make sure bolts are not getting loose? Retainer
nuts, lock washers, jamming nuts?

Thanks,
Alex

BTW Thrust ball bearing is not an option since I hope to eventually mass
produce this device so it must be really inexpensive


Thanks

If you use a nut with a nylon locking patch, you can control the screw
tightness without the screw working loose.
The other approach is to use a stepped bolt (aka shoulder bolt or stripper
bolt) and a wave washer to control the load.
A shoulder bolt can be replaced by a regular bolt and a length of tubing.

Erich

"Alex" wrote in message
m...

I am using a swing arm for my home made device.
It was inspired by the swing arm lamp like this one
http://www.lightspc.com/img/g-2518.jpg

My swing arm is made of 3/8 square steel tubes and Delrin plates. Tubes
are
attached to Delrin plates by 10-32 bolts.
I use steel washers against Delrin. That should give me low friction.

The problem I have is that it's hard to control bolts tightness. If it's
not
tight enough the whole swing arm has a significant "play"
If you tight it to much it's hard to move due to high friction.

Is there a good solution for this problem?

BTW: what should I use to make sure bolts are not getting loose? Retainer
nuts, lock washers, jamming nuts?

Thanks,
Alex

"Alex" wrote in news:FKsdb.6838$a46.2950
@newssvr27.news.prodigy.com:

http://www.lightspc.com/img/g-2518.jpg


Nylon locknuts would be my choice for the bolt tightness issue. (Nylock?)
I'm afraid with the delrin plates, control of the tightness is going to be
an issue. It is too slippery and deformable, in my opinion, to retain a
very specific clamping force. Probably why the lamp manufacturers use metal
plates for this.

--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

On Sun, 28 Sep 2003 04:02:04 GMT, "Kathy and Erich Coiner"
wrote:

If you use a nut with a nylon locking patch, you can control the screw
tightness without the screw working loose.
The other approach is to use a stepped bolt (aka shoulder bolt or stripper
bolt) and a wave washer to control the load.
A shoulder bolt can be replaced by a regular bolt and a length of tubing.

Erich

Thats what I would do. The problem with using only delrin, is its got
an odd "crush" limit and its either too slippery when loose, or it
suddenly reaches its elasticity limits and starts to crumple (sorta
kinda)

Gunner

"Alex" wrote in message
om...

I am using a swing arm for my home made device.
It was inspired by the swing arm lamp like this one
http://www.lightspc.com/img/g-2518.jpg

My swing arm is made of 3/8 square steel tubes and Delrin plates. Tubes
are
attached to Delrin plates by 10-32 bolts.
I use steel washers against Delrin. That should give me low friction.

The problem I have is that it's hard to control bolts tightness. If it's
not
tight enough the whole swing arm has a significant "play"
If you tight it to much it's hard to move due to high friction.

Is there a good solution for this problem?

BTW: what should I use to make sure bolts are not getting loose? Retainer
nuts, lock washers, jamming nuts?

Thanks,
Alex





"Anyone who cannot cope with firearms is not fully human. At best he
is a tolerable subhuman who has learned to wear shoes, bathe and not
make messes in the house."
With appologies to RAH..

How about using a spring washer of some sort (cone or wave type) in the
assembly to help you control the compression better? I would try this in
conjunction with an elastic stop nut (nylock).

Your Delrin washers may cold flow after awhile and get thinner though, which
might make it difficult to keep the compression constant.
--
Cheers,

--Mitch



"Alex" wrote in message
m...

I am using a swing arm for my home made device.
It was inspired by the swing arm lamp like this one
http://www.lightspc.com/img/g-2518.jpg

My swing arm is made of 3/8 square steel tubes and Delrin plates. Tubes
are
attached to Delrin plates by 10-32 bolts.
I use steel washers against Delrin. That should give me low friction.

The problem I have is that it's hard to control bolts tightness. If it's
not
tight enough the whole swing arm has a significant "play"
If you tight it to much it's hard to move due to high friction.

Is there a good solution for this problem?

BTW: what should I use to make sure bolts are not getting loose? Retainer
nuts, lock washers, jamming nuts?

Thanks,
Alex

What is the optimal solution for this problem than?
I guess thousands of people before me encountered this problem before and
successfully(at least some of them) solved it.



"Mitch" wrote in message
...
How about using a spring washer of some sort (cone or wave type) in the
assembly to help you control the compression better? I would try this in
conjunction with an elastic stop nut (nylock).

Your Delrin washers may cold flow after awhile and get thinner though,
which
might make it difficult to keep the compression constant.
--
Cheers,

--Mitch



"Alex" wrote in message
m...

I am using a swing arm for my home made device.
It was inspired by the swing arm lamp like this one
http://www.lightspc.com/img/g-2518.jpg

My swing arm is made of 3/8 square steel tubes and Delrin plates. Tubes
are
attached to Delrin plates by 10-32 bolts.
I use steel washers against Delrin. That should give me low friction.

The problem I have is that it's hard to control bolts tightness. If it's
not
tight enough the whole swing arm has a significant "play"
If you tight it to much it's hard to move due to high friction.

Is there a good solution for this problem?

BTW: what should I use to make sure bolts are not getting loose?
Retainer
nuts, lock washers, jamming nuts?

Thanks,
Alex

"Alex" wrote in message
m...

I am using a swing arm for my home made device.
It was inspired by the swing arm lamp like this one
http://www.lightspc.com/img/g-2518.jpg

My swing arm is made of 3/8 square steel tubes and Delrin plates. Tubes
are
attached to Delrin plates by 10-32 bolts.
I use steel washers against Delrin. That should give me low friction.

The problem I have is that it's hard to control bolts tightness. If it's
not
tight enough the whole swing arm has a significant "play"
If you tight it to much it's hard to move due to high friction.

Is there a good solution for this problem?

BTW: what should I use to make sure bolts are not getting loose? Retainer
nuts, lock washers, jamming nuts?

I hate those damn lights. They work well brand new but after a few doses of
chems on them they start to sag, droop and everything inbetween.

I dont know what kind of environment this is going to be used in but delrin
aint gonna last long if its going into a machine shop.

In any event you may want to look at hemi-spherical washers, nylock bolts
and such. Also, to where you are bolting it may make a difference. The swing
arm is bolted from the side which makes it conveinant but distributes the
clamping force from the side of the movement of the arm. To me it would make
more sense to have the bolt in parallel to the axial movement of the arm,
not 90 degrees from it.

Sort of along the lines of a wriggler set.

HTH

Bing

"Bing" wrote in
:


"Alex" wrote in message
m...

I am using a swing arm for my home made device.
It was inspired by the swing arm lamp like this one
http://www.lightspc.com/img/g-2518.jpg

My swing arm is made of 3/8 square steel tubes and Delrin plates.
Tubes
are
attached to Delrin plates by 10-32 bolts.
I use steel washers against Delrin. That should give me low friction.

The problem I have is that it's hard to control bolts tightness. If
it's
not
tight enough the whole swing arm has a significant "play"
If you tight it to much it's hard to move due to high friction.

Is there a good solution for this problem?

BTW: what should I use to make sure bolts are not getting loose?
Retainer nuts, lock washers, jamming nuts?

I hate those damn lights. They work well brand new but after a few
doses of chems on them they start to sag, droop and everything
inbetween.

I dont know what kind of environment this is going to be used in but
delrin aint gonna last long if its going into a machine shop.

In any event you may want to look at hemi-spherical washers, nylock
bolts and such. Also, to where you are bolting it may make a
difference. The swing arm is bolted from the side which makes it
conveinant but distributes the clamping force from the side of the
movement of the arm. To me it would make more sense to have the bolt
in parallel to the axial movement of the arm, not 90 degrees from it.

Sort of along the lines of a wriggler set.

HTH

Bing




I'm afraid with using the spring washers, (whether it be bellvelle or
wave), they will cut into the delrin over a short period of time.

Bellvelle washers are a great asset in many types of clamping fixtures,
especially if you want to control the clamping force accurately, or if
the parts are odd shaped. The variety and accuracy of the spring rates
available allow you to find just about whatever you need, (relatively
cheap too)



--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

Remove sp to reply via email

Alex,
You won't ever get good bolt stretch using special washers, plastic, etc.

This is the same problem you are having with the Delrin.
You need to remove it from compression in the joint.
It's stiffness is low compared to the bolt, so you are not getting any bolt
stretch (the goal).

A steel sleeve on the bolt to put stiff material between both ends is best.

A shoulder bolt will work, but you better use a lock nut, because you're
depending on the
ends of the threads to hold the nut on, rather than a good joint. Most lawn
mowers do this
for their wheels. Lock nuts are great for keeping you from digging all over
the back yard
looking for the nuts after they fall off, but don't contribute to bolt
stretch either.

Good luck.
Jim
Alex wrote in message
.com...
BTW Thrust ball bearing is not an option since I hope to eventually mass
produce this device so it must be really inexpensive


Thanks

Why not just use some springs to counter the torque like on the lamp
shown?
You are working with controlled opposite forces. There's a good reason
for all those stringy things in your arms and hands.
If you don't like springs you could use hood lifter nitrogen shocks.
Or larger diameter knuckles so the load at each joint is spread out and
easier to adjust

Alex wrote:
What is the optimal solution for this problem than?
I guess thousands of people before me encountered this problem before and
successfully(at least some of them) solved it.

Leather and cork are 2 traditional materials
for this application.




"Mitch" wrote in message
...

How about using a spring washer of some sort (cone or wave type) in the
assembly to help you control the compression better? I would try this in
conjunction with an elastic stop nut (nylock).

Your Delrin washers may cold flow after awhile and get thinner though,

which

might make it difficult to keep the compression constant.
--
Cheers,

--Mitch



"Alex" wrote in message
. com...

I am using a swing arm for my home made device.
It was inspired by the swing arm lamp like this one
http://www.lightspc.com/img/g-2518.jpg

My swing arm is made of 3/8 square steel tubes and Delrin plates. Tubes

are

attached to Delrin plates by 10-32 bolts.
I use steel washers against Delrin. That should give me low friction.

The problem I have is that it's hard to control bolts tightness. If it's

not

tight enough the whole swing arm has a significant "play"
If you tight it to much it's hard to move due to high friction.

Is there a good solution for this problem?

BTW: what should I use to make sure bolts are not getting loose?

Retainer

nuts, lock washers, jamming nuts?

Thanks,
Alex

On Sun, 28 Sep 2003 18:28:31 GMT, "AM" wrote:

If you made the plates out of metal instead of delrin, you could use low
friction washers(disks) between the arm and the plate.
I can't think of where I've seen this before, but I know I've disassembled
mechanical devices that used paper thin flat disks possibly made with teflon
at metal to metal pivot points.

Sounds like a fishing reel drag, although that would be somewhat
overbuilt. Still, a drag washer between flat metal surfaces, with
tension adjusted by threaded nut and belleville washers, would work
well.

Pete Keillor

Note that most commercial versions I have seen have a thumbscrew or wingnut
for adjusting the compression/ stiffness to taste - which also serves as a
periodic "tightener" when things start to wear a bit...
--
Cheers,

--Mitch

"Alex" wrote in message
...
What is the optimal solution for this problem than?
I guess thousands of people before me encountered this problem before and
successfully(at least some of them) solved it.



"Mitch" wrote in message
...
How about using a spring washer of some sort (cone or wave type) in the
assembly to help you control the compression better? I would try this
in
conjunction with an elastic stop nut (nylock).

Your Delrin washers may cold flow after awhile and get thinner though,
which
might make it difficult to keep the compression constant.
--
Cheers,

--Mitch



"Alex" wrote in message
m...

I am using a swing arm for my home made device.
It was inspired by the swing arm lamp like this one
http://www.lightspc.com/img/g-2518.jpg

My swing arm is made of 3/8 square steel tubes and Delrin plates.
Tubes
are
attached to Delrin plates by 10-32 bolts.
I use steel washers against Delrin. That should give me low friction.

The problem I have is that it's hard to control bolts tightness. If
it's
not
tight enough the whole swing arm has a significant "play"
If you tight it to much it's hard to move due to high friction.

Is there a good solution for this problem?

BTW: what should I use to make sure bolts are not getting loose?
Retainer
nuts, lock washers, jamming nuts?

Thanks,
Alex

I don't think you want low friction as much as wanting dynamic
friction and static friction coeficients to be fairly close to each
other. And the other thing you want is a spring element so that the
bolt does not have to stretch to provide the spring. A bellville
washer and a plain washer ( so the B. Washer does not cut into the
friction material ) should work well.
Dan


"Alex" wrote in message m...
What is the optimal solution for this problem than?
I guess thousands of people before me encountered this problem before and
successfully(at least some of them) solved it.

"Alex" wrote in message
...
What is the optimal solution for this problem than?
I guess thousands of people before me encountered this problem before and
successfully(at least some of them) solved it.



"Mitch" wrote in message
...
How about using a spring washer of some sort (cone or wave type) in the
assembly to help you control the compression better? I would try this
in
conjunction with an elastic stop nut (nylock).

Your Delrin washers may cold flow after awhile and get thinner though,
which
might make it difficult to keep the compression constant.
--
Cheers,

--Mitch



"Alex" wrote in message
m...

I am using a swing arm for my home made device.
It was inspired by the swing arm lamp like this one
http://www.lightspc.com/img/g-2518.jpg

My swing arm is made of 3/8 square steel tubes and Delrin plates.
Tubes
are
attached to Delrin plates by 10-32 bolts.
I use steel washers against Delrin. That should give me low friction.

The problem I have is that it's hard to control bolts tightness. If
it's
not
tight enough the whole swing arm has a significant "play"
If you tight it to much it's hard to move due to high friction.

Is there a good solution for this problem?

BTW: what should I use to make sure bolts are not getting loose?
Retainer
nuts, lock washers, jamming nuts?

Thanks,
Alex


Alex,
The belleville washers others have suggested are a good option. A few
things to know. They come in different spring rates, by varying the
thickness. They also can be stacked. When stacking two with the cones the
same way the spring rate will double. Flip one over so the cones are
opposite and the travel doubles while the spring rate is cut in half. This
will keep a more constant pressure over a greater range of wear. You want
to use them with a flat washer against the delrin as the brake surface.
That way the bellevilles won't dig in and the tension will stay constant for
a very long time. Use the Nylon licking nut to keep the nut from working
loose.

Gary H. Lucas

ERich10983 wrote:

same way the spring rate will double. Flip one over so the cones are
opposite and the travel doubles while the spring rate is cut in half.

Doesn't the spring rate stay the same?

Nope. Consider: Spring rate is force change per unit distance. When
you put two springs of the same rate in series, be they Bellville or
coil, each one only moves half as far for a given total displacement.
The delta-F is therefore half.

Ted