Shaft material for slot mortiser using bronze bearing

[Jim Lischio]

I'm looking to build a sliding table for a slot mortiser. I have some ball bearing drawer slides, but I saw these mounted bronze bearings at McMaster-Carr and heared of something similar being used to a router lift, but the chrome plated shaft material is pricey. Do I need to use the expensive shaft material for this purpose or is there an inexpensive alternative that would be suitable for this purpose? Or am I better off using the drawer slides. I have also been keeping an eye on the 8020 Garage Sale, but I can't seem to find the housing, pads, and extrusion available at the same time.

http://farm3.static.flickr.com/2036/2105237963_36fb194c03_o.gif

Thanks,

Jim

[Greg Cole]

FWIW, the shaft material is normally a thin coating or case hardened for a good reason, to wear the parts that are supposed to wear ie bushings etc and not the shaft... I know from the day job cutting threads etc in the case hardened stuff is a definate challenge unless you have metal working tooling & experience.
Whether you opt to buy the good shaft material or not is up to you, depends on how much use these shafts would see. I think you'd most likely be fine with the non hardened material, just make sure you get shaft material as it's ground to a certain smoothness for finish and usually much straighter that simple round stock.
Worth the price of admission.

Greg

[Lee Schierer]

I agree with Cole. The chromed hardened ground shaft material is held to tighter tolerances than plain round stock.

[Rod Sheridan]

Hi Jim, do you intend to use these pillow blocks to allow a shaft to slide back and forth, or are they to allow the shaft to rotate?

Plain bearings are only suitable for rolling loads, since the shaft is supported by a wedge of oil that forms between the shaft and the bearing, the two metal pieces never touch except during start up when the wedge is forming. This gives plain bearings a very long life in some applications.

If you intend to use the bearing to slide a shaft back and forth on, no wedge will form, and the bearing will have a groove worn in it.

That's why sliding loads either run in ways with replaceable wear strips, or use rolling element bearings such as in linear bearings for slide application.

That said, you may be OK for limited use at home, although I'd choose a different bearing if it's for a sliding application.

Regards, Rod.

[Gary Ratajczak]

I agree with the earlier comment on the bearing style you show. You would be better off with bearings that are mounted to a piece of aluminum angle stock, and ride horizontally along the shaft.

Also, i built an air operated pocket hole machine, and used the Drill Rod from McMaster. It isn't as fine a tolerance as shaft stock, but much better than cold rolled from big box.

[Jim Lischio]

Thanks for everyone's suggestions so far. I was planning on having the bearings slide along the shaft (rather than rotate) and I do not want to wear grooves in the shaft material, so I guess I should keep looking. I am just a hobbiest, so the jig will not be used daily, but I would like it to be accurate and last for a while, but not cost a lot, otherwise I will look into a Domino. I have read that linear bearings are overkill for this application, but am not knowledgable enough to know what is appropriate, so all suggestions are welcome (the more specific the better).

Jim

[Mike Marcade]

What about using a linear bearing? Mcmaster carry these too.

http://www.b2b-linearbearing.com/rimages/464/linear-bearing-02-02.jpg

[Jim Lischio]

It looks like the 10 series parts from 8020 Garage would run about $110 + screws and shims and the 15 series would be ~$150. I planned on using 8 pieces of housing, 24 bearing pads, and 6' of extrusion. They don't have the double flange housing in the 10 series right now, so I would have to get the single flange- could this be turned on it's side to leave an open slot on the opposite horizontal side and the extrusion raised off the base using some blocks? I am not sure what the comperable setup would be/cost using pillow block bearings and steel shaft from McMaster (would 1" shaft material be suitable?). 6' of 1" diameter case hardened steel runs $66, plus ends and I am not sure which bearings.

Jim