Re: [CAD_CAM_EDM_DRO] ACME ( was Re: leadscrew, acme screw, threaded rod, ballscrew

turbulatordude wrote:

>you commented that this is slop, but slop typically implies
>hysteresys or backlash.
>

Ya, I was not choosing words very well..... I do that once in a while. I
jumped ahead of myself relating the "slop" to the fiddling around people
do to make decent nuts for conventional acme that do not need to be
adjusted all the time. I would not bother using backlash adjustments in
a control ever, unless there just is no other way. Personally, I'd
rather encourage people to do it as close to "correctly" from the get-go
than to end up building two machines because the first one could never
live up to expectations. But that is human nature.... We're Saving
money, but doing it twice ! I find that when I think I am saving, I run
the numbers and find out I spent twice as much.

MY recommendation for those who desire to LEARN first, is just to
"downsize" their dream, but keep the quality way up there. This way when
they are all done learning, they STILL have an excellent machine, just a
bit too small. The beauty is that the components will be short and
stubby, thus the Cost to build will be too. (12" of THK is a lot
cheaper to find than 10 footers ! So, the "learning" by using garage
door track, and manure spreader chain just because it is cheap is never
the one I recommend.. Do it right the first time. Nothing stops anyone
really......
(you can see the hysteresys coming out again right ?)

>This type of error has no real meaning in a lot of the wood routers
>and other hobby stuff so a really poor screw with 0.015"/inch would
>be repeatable.
>

Well, maybe, Unless the crappy Nut inserts more "Slop"..... That was my
whole line of thought... There are two screws to use to obtain the best
results.... One with an antibacklash acetal nut, or the more expensive
ball screws. I just have been soured on any computer powered application
using Acme or all thread. Fine to adjust your wood planer head up and
down with a crank, thats about it.

>we don't often talk about temperature and humidity as inducing
>errors, but a cold shop, 50 degrees will have different
>charasteristics from a hot shop 90 degrees.
>

Absolutely ! Had a boss once that turned the heat down to 35F every
night. Machines made junk right up till 1/2 hour before quiting time !
Boy, were we saving money !

> this is another place
>hysteresis comes into play. some nuts may become more elastic at
>higher temperatures and oils may become thicker at colder
>temperatures. these will be errors that cannot be adjusted out.
>

We used to run a toolpath in air for a first pass on a cold machine with
Acetal type nuts. But really, we could not measure any differences
between the two when one was done one way, and one the other. Now we
just cut. I think the composites they use run about the same provided
they are not being overdriven creating unecessary heat. Everything has
limits..

>like you mentioned Precision modified-ACME have better than 0.003"
>and have a smoother finish to reduce friction. These are along the
>lines of the best ACME are better than the worst ballscrew comment I
>made.
>

Kerk guys ( if you believe every salesman) told me that those rating
really are the extreme so they cover their butts. Those style screws
come under a whole lot more scrutiny when being manufactured than acme,
and that is what you see in the price> $38 vrse $128 for 6 foot. Worth
every dime.
You can call them and they will find a higher rated screw for more $$$

>Bottom line is to use what you REQUIRE.
>

That is exactly the point, However, when you say:

> don't buy linear rails and
>anti-backlash ball nuts if you are making wooden signs or home
>circuit boards.
>

I get the willys,,,, Maybe if the letters are at least 3" high.... I do
plenty down to the .080" neighborhood and there can be a lot of funny
looking letters if things are not really tight. Nothing more annoying
than "steps" along an edge, overruns on corners..... So, sorry,
skateboard wheels on cold rolled steel won't fly here. I say GET the
True linear components and spend lots of time figuring out how to mount
them straight and square, and to get the machine perfectly level and
aligned. The bigger the machine, the harder it gets. If you do not have
some sort of true linear component to work with, It must be a bumpy
ride.Some of these guys with 6' X 15' flatbed router building ideas are
better off buying a clean used machine. and they are out there.

But like you said... It has to be what you need.

CL