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Linear Bearings
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nicholaslieurance
Fri, 30 Jan 09 15:04:32 +0000
I've noticed many people using aluminum extrusions from 80/20 or MK
profiles for their CNC frames. However, no one seems to be
incorporating the UHMW linear bearings from these companies.
Instead, most are using ball bearings and steel shafts.
Wouldn't the plastic bearings be more suitable for dusty and dirty
machining environments? Don't they provide smooth enough motion for CNC
machining?



6 replies folowing
djdever
Fri, 30 Jan 09 21:48:27 +0000
--- In DIY-CNC@yahoogroups.com, "nicholaslieurance"
wrote:

>
> I've noticed many people using aluminum extrusions from 80/20 or MK
> profiles for their CNC frames. However, no one seems to be
> incorporating the UHMW linear bearings from these companies.
> Instead, most are using ball bearings and steel shafts.
> Wouldn't the plastic bearings be more suitable for dusty and dirty
> machining environments? Don't they provide smooth enough motion for CNC
> machining?
>


I think these UHMW bearings lack the overall performance needed for
many machine motions. You can shim them to decrease clearances but
you sacrifice ease-of-movement. So you tend to fight speed, load and
precision versus employing other linear guides (bushing, frelon
bushing, ball or roller bearing, etc.).
-D

dicsEE
Fri, 30 Jan 09 22:40:48 +0000
 
Steve Blackmore
Fri, 30 Jan 09 22:40:48 +0000
On Fri, 30 Jan 2009 15:04:32 -0000, you wrote:

>I've noticed many people using aluminum extrusions from 80/20 or MK
>profiles for their CNC frames. However, no one seems to be
>incorporating the UHMW linear bearings from these companies.
>Instead, most are using ball bearings and steel shafts.
>Wouldn't the plastic bearings be more suitable for dusty and dirty
>machining environments?


> Don't they provide smooth enough motion for CNC
>machining?


They are fine - They outlast the ball bearing slides in dusty and dirty
locations far better. I've seen them used on CNC Lasers and routers to
good effect.

Lasers leave a deposit on the rails over time if the extract isn't that
good, wood router dust get's everywhere, both will clog the bearings and
they start to skate, rather than roll. Even units with seals succumb
after a while. I've used the Igus Iglide split bearings on a router to
replace ball bearing slides on round rails that failed after a few
months, they are still working well over a year later with no
maintenance or lubrication whatsoever.

Steve Blackmore
--
Gary Corlew
Fri, 30 Jan 09 23:49:39 +0000
I tried them on my first cnc router build, Once I got them tight enough so
they were not rocking or racking my steppers could barely drive the gantry.
I now have linear bearings and rails, I can push it with the slightest
pressure from a finger.



From: DIY-CNC@yahoogroups.com [mailto:DIY-CNC@yahoogroups.com] On Behalf Of
nicholaslieurance
Sent: Friday, January 30, 2009 10:05 AM
To: DIY-CNC@yahoogroups.com
Subject: [DIY-CNC] Linear Bearings



I've noticed many people using aluminum extrusions from 80/20 or MK
profiles for their CNC frames. However, no one seems to be
incorporating the UHMW linear bearings from these companies.
Instead, most are using ball bearings and steel shafts.
Wouldn't the plastic bearings be more suitable for dusty and dirty
machining environments? Don't they provide smooth enough motion for CNC
machining?





[Non-text portions of this message have been removed]

Steve Blackmore
Sat, 31 Jan 09 01:01:35 +0000
On Fri, 30 Jan 2009 18:49:39 -0500, you wrote:

>I tried them on my first cnc router build, Once I got them tight enough so
>they were not rocking or racking my steppers could barely drive the gantry.


They weren't set up and adjusted correctly then.

Steve Blackmore
--
Gary Corlew
Sun, 01 Feb 09 13:59:05 +0000
That is exactly what happened to me. Once I got them shimmed enough to
remove racking and tilting it would only move at 10 ipm, needless to say a
router needs to run a lot faster than that. It also used a -10 tpi acme
screw which was down the center, at first I was thinking of going to two
screws but decided against that because the racking problem would be solved
but would still have to run the uhmw slides tight to prevent tilting, the
only resolution I could come up with for the tilting was to buy more 80/20
aluminum extrusions and more uhmw slides pouring more and more money into
something that was a bad idea in the first place. I got rid of it all I went
with VXB linear slides and ball screws, It went to 50 ipm, I realize that
the crews and ball screws are different pitches and that was part of the
performance gain but the slides from VXB was responsible for a good portion
of it. Another performance enhancer I did was going to gecko 203v drives and
bigger power supply, It can now run at 150 ipm all day long. Most of the
time I use .25 router bits and they should be run at around 130 ipm I
actually make chips now and not dust, much better health wise. And yes I
have a dust collector also hooked up to it. When I want to cut something the
last thing I want to do is spend time spraying everything down with Teflon
spray just so it will move reliably, I want to cut! I machine a lot of
aluminum at work, I just finished a job for the US navy the tolerance was
+.002 0.00 at 68 degrees it had to be machined at this temp and checked at
this temp, one day my boss decided to shut off the heat for the night.
Aluminum changes a lot due to temp variations, the next morning I was way
out of tolerance, I told him about the errors of his ways and proved my
point by using our faro arm on it and giving him the report, it took about
two hours to get the temp back up.



From: DIY-CNC@yahoogroups.com [mailto:DIY-CNC@yahoogroups.com] On Behalf Of
djdever
Sent: Friday, January 30, 2009 4:48 PM
To: DIY-CNC@yahoogroups.com
Subject: [DIY-CNC] Re: Linear Bearings



--- In DIY-CNC@yahoogroups.com ,
"nicholaslieurance"
wrote:

>
> I've noticed many people using aluminum extrusions from 80/20 or MK
> profiles for their CNC frames. However, no one seems to be
> incorporating the UHMW linear bearings from these companies.
> Instead, most are using ball bearings and steel shafts.
> Wouldn't the plastic bearings be more suitable for dusty and dirty
> machining environments? Don't they provide smooth enough motion for CNC
> machining?
>


I think these UHMW bearings lack the overall performance needed for
many machine motions. You can shim them to decrease clearances but
you sacrifice ease-of-movement. So you tend to fight speed, load and
precision versus employing other linear guides (bushing, frelon
bushing, ball or roller bearing, etc.).
-D





[Non-text portions of this message have been removed]

Steve Blackmore
Sun, 01 Feb 09 14:17:16 +0000
On Sun, 1 Feb 2009 08:59:05 -0500, you wrote:

>That is exactly what happened to me. Once I got them shimmed enough to
>remove racking and tilting it would only move at 10 ipm, needless to say a
>router needs to run a lot faster than that.



I've got Igus Iglide ones running at 5m/min on a router, which is the
max it will do because of screw pitch and pulse choice and the lasers
run at 100m/min. It's down to who's bearings and the type of rails. The
router is on chromed rails and the laser's are on stainless.

Steve Blackmore
--