Re: [CAD_CAM_EDM_DRO] Re: no thrust bearing

On Fri, 18 Apr 2003 19:20:37 -0000, you wrote:

>Hi Bob, list,
>
>While not impossible, it is not like walking into Walmart/RadioShack
>when one wants to purchase things like linear rails, leadscrew, etc.
>The plans I am looking at uses drill rods for guide. No one here
>seems to know what a drill rod looks like.

www.mcmastercarr.com They have drill rod and acme threaded rod.

If you need (inexpensive) ball bearing assemblies, go to the local
super sports store and find a bearing replacement kit for inline
skates. 8 mm inside (it is metric) and 22mm outside (iirc).

Standard acme nuts are relatively inexpensive, anything else becomes
hard on the wallet.

>
>So, just to dip my toes in to find out what it is all about, I may
>try to make something simple with drawer slides and threaded rods
>which one can easily pick up at the hardware stores, then perhaps
>become more ambitious later. (I know there are lots of "professionals
>here, but anyone else went down this road in their "formative" years?)

Yes. Anything smaller than 1/4 inch is probably bent. Avoid the
zinc plated rod, get oil finished. You'll be paying through the nose
for it, though. I might (one day) finish the really large tables I
had in mind, they might be for a cnc router.

The slides are decent, but there is an alternative... you might want
to try an assembly with square tubing for rails, you notch the end
pieces at a 45 degree angle to angle the tubing. You then take a
piece of angle bracket, and attach ball bearing assemblies to that so
that the outer races run on the edges of the square tubing. This
might be a relatively easy task with a good mill or drill. Not
precision, though. I'd make the system such that it can adapt to a
changing table height so it knows the profile of the table. We're
probably talking 1/64th of an inch accuracy, not 0.001...

>
>How does one attach a leadscrew/threaded rod to a thrust bearing?
>Does one just make sure that the diameters are a tight fit, or are
>there screws to tighten or something?

Probably not screws, but you might use a collar, which then forms the
surface pushing against the thrust bearing.

Many people use a flexible coupling of some sort, since it makes the
stepper alignment a little less critical.


Harvey

>
>Thanks
>
>In CAD_CAM_EDM_DRO@yahoogroups.com, "Robert Campbell" <bob@c...>
>wrote:
>> Andrew,
>>
>> Look at my web site and look in the section on machined parts.
>> www.campbelldesigns.com
>>
>> Look at the bearing blocks that I use. What I do is to use two
>radial
>> bearings with a lip on them and press one in from both sides of the
>bearing
>> block.
>>
>> I do this at both ends. On the far end, I preload the bearings
>with a
>> threaded end and a nut.
>>
>> On the stepper motor end, I use a flexible coupler to connect the
>lead screw
>> to the stepper motor.
>>
>> To answer you question, I would always use bearings in some type of
>bearing
>> block. You will also need to use a nut on at least one end of the
>screw.
>>
>> Bob Campbell
>> ----- Original Message -----
>> From: "andrewyslee" <andrewlee@s...>
>> To: <CAD_CAM_EDM_DRO@yahoogroups.com>
>> Sent: Thursday, April 17, 2003 8:09 PM
>> Subject: [CAD_CAM_EDM_DRO] no thrust bearing
>>
>>
>> > Hi,
>> >
>> > I am looking at some plans which have the leadscrew hanging free
>at
>> > one end and directly connected to the stepper motor shaft end at
>the
>> > other. I had read in previous post about thrust bearing, and
>vaguely
>> > remembered someone mentioning that the stepper motor bearing
>cannot
>> > take axial load. However, I was also told that if I am not cutting
>> > metal, I wouldn't be dealing with very high forces.
>> >
>> > Will connecting leadscrew directly to stepper motor shaft lead to
>> > much shorter motor life?
>> >
>> > Thanks
>> >
>> > Andrew
>> >
>> >