Acme thread through bearing -- OK?

[RicknBeachcrest]

I am planning on using Acme lead screws for the X and Y and was wondering if it was standard practice to just run the screw through the bearing?

Or would you connect the stepper to a drill rod then through the bearing and then connect to the Acme screw?

It sure would make it easier to just run the the Acme lead screw through the bearing, but there would not be as much surface contact as a drill rod would provide.

Thanks.
Rick

[packrat]

Most screws are turned down to fit the bearings and the coupler. Unless I misunderstood what your asking. You do mean the support ends of the screw, right? How would you connect a drill rod to the screw?

Usually the end connected to the motor has double bearings. To prevent putting a end load on the motor shaft.

[ger21]

I am planning on using Acme lead screws for the X and Y and was wondering if it was standard practice to just run the screw through the bearing?

"Standard Practice" varies, depending on who you're asking.

I prefer turning the ends, some use the drill rod method, and other just run the screw through a pillow bock bearing.

[RicknBeachcrest]

Well as they say about a picture...

I was referring to the the bearing block pointed to by the red arrow. But this could also be carried further to the bearing block (at the end of the screw) pointed to by the blue arrow. It sure would be easier not to have to turn down the end of the screw. And it would be easier not to have to put a piece of drill rod in between the stepper and the bearing block (red arrow).

This is a photo of Senna's (Steve's) router. Great build Steve. I think this is the design I will be using in my build.

Rick

[dave22]

Originally Posted by RicknBeachcrest Well as they say about a picture... I was referring to the the bearing block pointed to by the red arrow. But this could also be carried further to the bearing block (at the end of the screw) pointed to by the blue arrow. It sure would be easier not to have to turn down the end of the screw. And it would be easier not to have to put a piece of drill rod in between the stepper and the bearing block (red arrow). This is a photo of Senna's (Steve's) router. Great build Steve. I think this is the design I will be using in my build. Rick

From the attached photo, I would use the following;
At the blue arrow - bearing block with a simple radial bearing to match the screw O.D.

At the red arrow - a stop collar - washer - thrust bearing - washer - bearing block with a simple radial bearing to match the screw O.D. - washer - thrust bearing - washer - a stop collar.

The screw protruding through the bearing assembly at the red arrow, can easily be connected to a motor shaft with a ACME screw coupler from dumpsterCNC. No drill rod required and no turning down of the screw end required.

Browse the pages of dumpsterCNC, here is a link: dumpsterCNC - anti-backlash solutions for home and industrial linear motion

My personal preference would be, to turn down the screw end. This allows me a wide choice of coupling methods - Lovejoy - Oldham - Helical - etc.

Hope this helps and Good Luck with your build.

[mlabruyere]

Some folks use the drill rod coupled to the screw method to limit the amount of "wasted" screw. I don't think it is generally a "best practice" just a preference.

I just run the screw through the bearings. I figure less connections in the drive line the better.

[RicknBeachcrest]

Originally Posted by mlabruyere I just run the screw through the bearings. I figure less connections in the drive line the better.

That was my thinking also.

[eigstein]

if you are going to use 3 pc. thrust bearings on both sides of the bearing block . the drill rod gives a better seat for the thrust bearings . i believe that was ahern's intent but not explained in enough detail .

[jsheerin]

Yes, acme rod through a bearing works fine as long as you fix the stationary thrust washers so they don't touch the screw. Using Ahren's parts, these are the washers against the block that holds the radial bearing. If they touch the screw, they can carve a notch in it - bad news. I glued mine to the bearing block and haven't had any problems since. The better solution would be to have a pocket in the block to locate the washers.

[DonFrambach]

For my router, which is nearly complete, I just ran the lead screws through the bearing blocks to the shaft couplers. That was a simple connection which avoided an additional connection which could potentially slip. I used metal shaft collars from CNCRouterParts.com for two axes and delrin collars from DumpsterCNC for the third axis. The delrin parts are threaded to match the lead screw the metal collars just clamp on. Both seem to work fine.

I am no expert, but it seems to me that a properly adjusted lead screw will place a great deal of axial force upon the collars (and thrust bearings) and essentially no radial force on the radial bearings. In addition, the radial bearings are steel and the lead screw is hardened steel. For these two reasons, I expect little wear on the lead screw or the bearings. Time will tell.

Here's some photos:
the first shows my Y axis with delrin connectors
the second shows my Z axis with steel and aluminum connectors
the third shows a lower power view of the Z axis after excess leadscrew was removed

[mlabruyere]

The first photo Don shows is exactly how mine are setup. I have bearing blocks at either end of the screw with the thrust washers and bearings for the axial loads pressed against the blocks with collars. Have had no problems since I built the CNC over a year ago.

Mine isn't as clean anymore but it works great!

[juzwuz]

Originally Posted by dave22 From the attached photo, I would use the following; At the blue arrow - bearing block with a simple radial bearing to match the screw O.D. At the red arrow - a stop collar - washer - thrust bearing - washer - bearing block with a simple radial bearing to match the screw O.D. - washer - thrust bearing - washer - a stop collar. The screw protruding through the bearing assembly at the red arrow, can easily be connected to a motor shaft with a ACME screw coupler from dumpsterCNC. No drill rod required and no turning down of the screw end required. Browse the pages of dumpsterCNC, here is a link: dumpsterCNC - anti-backlash solutions for home and industrial linear motion My personal preference would be, to turn down the screw end. This allows me a wide choice of coupling methods - Lovejoy - Oldham - Helical - etc. Hope this helps and Good Luck with your build.

Hi! I bought acme screws, delrin nut, and 2 bearing blocks from here:

http://www.precisiontechmachining.com/id1.html

but I just realized I only have radial bearings and nothing to support the axial loads. Can I use the thrust bearings and stop collars from cncrouterparts or do I need a different size since the ends of the screws are turned down?