[Alchemist29]

I am considering building my first machine. In the beginning it's going to be a simple 3-axis machine with a router for the spindle, but I also plan to eventually add a A/B axis with a Dremel-clone style tool for the spindle to do fine detail work in wax for jewelry casting.

My question is this: on a 5-axis machine, you have a bearing that rotates on a plane parallel to the table. I normally know this as a lazy susan bearing, but I know that's not the correct name for the mechanical part. What do you call this bearing? Is it a thrust bearing?

[keebler303]

Try "slewing ring bearing"

You want your bearing to resist loads in all directions. There are multiple ways you could achieve it.

Matt

[Al_The_Man]

Also could be a Thrust Bearing, these come in a few forms and can require a preload setting.
If it revolves around the Z, it would be a 'C' Axis.
Al.

[JerryBurks]

Something like this?. They actually do call it a Lazy Susan Bearing.
Not sure how precise they are. But regular large low profile ball or needle bearing can be pricey.

[keebler303]

Something like this?. They actually do call it a Lazy Susan Bearing.

Being that the races are made of aluminum, I doubt it would be up to high accuracy CNC type use.

Matt

[louieatienza]

You'd want a thin-section anglular contact bearing... actually, two per axis. They're normally not cheap, (especially if bought as a matched pair) but you can find them on eBay as surplus. For a light duty machine for wax you might be able to use two thin-section radial bearings with a very light preload.

[Alchemist29]

My next question was going to be whether or not one of the inexpensive 3" steel lazy susan bearings that are rated 500 pounds like you get from Home Depot would work for a small machine.

These bearings are made for chairs, so they might have too much play in them for a cnc.

I suppose if I could get a 3 axis machine running, I could always machine my own bearing...

[louieatienza]

They might hold 500lbs of weight (spread across dozens and dozens of bearing balls it seems logical) but it may have play. Definitely not good for jewelry work. Machining your own might not work too well with a 3 axis since the circles would be interpolated; even cheap radial bearings would probably have more accurate races.

[wizard]

Old Bullard type vertical turret lathes made use of huge Timken like bearings. Of course that being a vertical turret lathe the axis had a lot to support. Depending on the intended usage though you may have a plain type bearing surface similar to ways on a machine. In the end there are many ways to skin a cat here, it all depends upon the needed performance.

In the case of machining wax though you probably can get buy just fine with angular contact bearings. There is really no sense in over designing.

[Alchemist29]

Would something like this be suitable?

[keebler303]

Would something like this be suitable?

No.

Bearings like that have a spherical outside surface so they can rotate in the housing to accommodate misalignment, that would allow your rotary axis to tilt off of true. If you're looking to do it on the cheap you could consider something like a trailer axle hub or even a hub off of a car. That would give you a pair of tapered roller bearings and plenty of rigidity, but the accuracy may not be up to par, it really depends on what your requirements are.

99 1999 Jeep Wrangler Crown Front Axle Hub Assembly 53007449 for - Auto Parts Network

Matt

[Al_The_Man]

The other thing to consider is how you intend driving this axis?
Al.

[Alchemist29]

I have a couple of wheel hub bearings off a pontiac aztek, but they are huge compared to what I envision the head to be. Surely there's a way to do this without the bearing weighing more than the little spindle....

[Lee DeRaud]

The other thing to consider is how you intend driving this axis?

Pretty much has to involve some kind of shaft...any reason he can't use the cheap/sloppy lazy-susan widget to support the axial load and a couple of standard ball bearings for the radial loads?

[Alchemist29]

Well, as far as driving the axis, I was thinking of having a large gear above, below, or in between the bearings and having a stepper motor drive it with a timing belt.

[louieatienza]

Check here:

Thin Section Bearings: VXB.com Ball Bearings

[wizard]

I refreshed my memory and took a deeper interest in this:

…a Dremel-clone style tool for the spindle to do fine detail work in wax for jewelry casting.

If you are machining wax in jewelry sized parts you most likely don't need a huge axis and the ability to withstand massive amounts of torque. As such a small set of angular contact bearings ought to do the job. Even more standard ball bearings would likely do the job with a light axial preload.

I have a couple of wheel hub bearings off a pontiac aztek, but they are huge compared to what I envision the head to be.

Immnot familiar with the specifics of the Pontiac but one of the guys in the sh
Op rebuilt the front end of his car and changed the wheel bearings. Those bearings would likely make a good choice if the accuracy was acceptable. In this case the bearings weren't of the Timken type but rather more of a ball bearing. Yes the cartridges are big but worth considering if they can be worked into your mechanical design. If not personally I'd go with a set of angular contact bearings.

Surely there's a way to do this without the bearing weighing more than the little spindle....

Get on line with a bearing manufacture and download a few catalogs. You can get rather small angular contact bearings. However I'd resist going to small. Figure out how big the working area will be on the spindle. Make sure you spindle shaft is reasonably robust to support that work areas.

You might also want to look into harmonic drives. Expensive at first glance but they could provide almost all that you need for this size or class of parts.

[Alchemist29]

I think the axial bearings give me a starting point. perhaps a combination of an axial and a normal rotary bearing.

[JerryBurks]

So how is the whole thing going to work, anyway? Are you building a 5-axis trunnion table?

For that matter, I have a new Sherline 72:1 rotary table with stepper adaptor sitting unused. Please PM if interested. I guess it would take care of the bearing and reduction need as well.

[Alchemist29]

I am terrible at sketching stuff, but let me see if I can explain it in less than 1000 words...

The "wax carving" head will have a circular pivot with an inverted U shaped bracket attached. There will be either a gear or timing belt mechanism driven by a stepper to rotate that U shaped bracket. Inside that U-Shaped bracket there will be a structure that holds the mini spindle. There will be a stepper that rotates the entire spindle bracket along an axis parallel to the table. That should allow the cutting bit to go from perpendicular to the table all the way to parallel to the table, if not further.

One of the things I want to be able to do is carve rings, so I'm also thinking about making an indexing rotary device where I can take a wax ring blank, size the interior with a sizing carver, put the blank on an appropriately sized dowel and fasten this to the indexer.

The normal 5-axis should allow the cutting head to add curved surfaces to the band of the ring, carve the top, etc. The rotary indexer will allow the carving head to carve all the way around the band of the ring, if desired.