HDPE Bearings

[jhowelb]

Has any ever tried HDPE Bearings or any other plastic operating in much the same fashion as the cast iron slides on a lathe or other machinery using dove tails?

What kind of performance would one expect, advantages, disadvantages, problems, etc.?

[Geof]

Originally Posted by jhowelb Has any ever tried HDPE Bearings or any other plastic operating in much the same fashion as the cast iron slides on a lathe or other machinery using dove tails? What kind of performance would one expect, advantages, disadvantages, problems, etc.?

HDPE is a bit softish. It slides very nicely and does not need lubricant but it will have flexibility due to the plastic compressing. It can also flow a bit or take a set from a constant heavy load.

UHMW is much better, much firmer, will not flow and does not take as much of a set with a constant load.

Delrin is possibly the best, but by far the most expensive. It is very rigid, does not flow, does not take a set, just needs a little white grease for lubrication (I have used Vaseline). Easy to work and strong enough to take threads.

Turcite is a variation on Delrin and it is made for machine ways.

Another fairly good plastic is the phenolic like used for electrical equipment. The stuff that is brown and looks like layers of fabric embedded in a plastic resin. Stinks horribly when being machined and the dust can cause allergies.

When you are using any of these on dovetail ways it is probably best to have thin pads supported by metal dovetails. Certainly HDPE and UHMW are not stiff enough for the dovetail itself. Delrin and phenolic could be but these are expensive so you may need to economise on how much is used.

[jhowelb]

Thanks for the thoughtful and thought filled response.

What I'm thinking of would be a light duty and seldom used moving gantry type router for cutting images into acrylic and sometimes wood. Skate bearings are just more hassle than the project would warrant. This would really be more of a toy than a tool. I already have a converted HF mill/drill for more serious work.

One possible slide design that occurred to me would amount to a V shaped slot cut into the plastic bearing material riding on a "rail" of angle iron. Not high speed and not heavy cutting for certain.

Any additional thoughts?

[Geof]

Angle has a really grungy surface finish. Although if you are using HDPE or UHMW maybe aluminum angle would be okay with the nicer finish. I have used UHMW and Delrin on round bar a few times but the only time I used angle it was stainless steel and the application was not precise or anything; it was also running partly immersed in seawater.

[jhowelb]

Heavy gauge alum. angle is do-able or even an arrangement with some CRS of some configuration. Angle came to mind because it would simplify alignment in this application. (I'm thinking of using a discarded iron table saw as a base to build on.)

A plug of plastic or brass under a set screw in a threaded through hole is being considered also.

The Gingery lathe used Alum. against CRS with some success so that is also a consideration.

Anyway, just ruminating!

Thanks!

[Geof]

Originally Posted by jhowelb ..... (I'm thinking of using a discarded iron table saw as a base to build on.)...

That is an interesting concept. Years ago I built a manually operated router using the aluminum base from an optical instrument; like the table saw it provided a nice flat surface to work from. I used round bar bolted along the edges with split Delrin bushings in split aluminum housings to carry the gantry; it was only 20 inches wide. The Y axis was also round bar. It worked like a charm for years cutting 3/16" wide slots 1/16" deep across aluminum flat bar clamped onto the aluminum base.

[jhowelb]

Imagine, if you will, two lengths of 1/4 X 2 SRC flat bar extending off opposite sides of the table. Four "C" shaped fixtures surrounding the outboard edges of the CRS with the pictured little buggers against the edges, top and bottom.

The gizmos I've found are made of delrin with stainless balls. A set screw with some sort with a mds filled nylon plug might do it too.

[jhowelb]

Sorta like this, maybe.

[Geof]

The only problem with that is that you have a small area in contact; with a ball it is very small. You may find that the balls indent into the steel flat bar.

That idea with setscrews behind brass plugs would probably work. Can you get brass threaded rod? Cut short pieces, screw them into your tapped holes and have a nut behind to lock them. You could have several in a row and adjust them for very nice sliding clearance, and adjust for wear.

Actually you don't need threaded rod, get some brass bolts and use them head down to get a larger sliding surface. You may need to finish the head to a smooth surface but that could be done even with a file.

[jhowelb]

With the mill and lathe (cnc both) I can manufacture almost anything, but the thought of others on the zone following a pattern also occurred to me. Among the reasons for the project is to interest and teach the Ukrainian kid our family has adopted. Adjustments and simplicity would be desirable.

Pre-made brass bolts have an appeal. Head smoothed off and faced square mounted head down as you suggest and on the other end a "jammed" nut and a stop nut for adjusting could be just the ticket.

[LeeWay]

I bought some nice heavy duty drawer slides from Surplus Center very cheap for the pair. These were pretty heavy steel and many steel balls. Probably Govt. or Military grade. There really wasn't any slop to speak of. I used these on some heavy duty drawers filled with nuts and bolts and things in a pickup truck box mounted on the back of the bed. Drop the tail gate and the drawers would slide open. They were latched too. My point is for some small machines, these things are really great ready made slides that can hold pretty good tolerances and take up very little space. I only gave a couple bucks a pair. Just something to consider.

[jhowelb]

I have considered drawer slides but have run against a number of concerns.

Over hang in machine tools is one cause of chatter. A drawer slide that started out at say 26" and extended to 52" will have a 26" over hang unless you use a second reversed slide.

Used on the Y axis for example a router bit will have 26" of movement with 52" of slide assembly. If things are centered there will be a 12.5" weapon protruding from each side of the machine just itching to whack you as it passes by.

I suspect that a slide will be relatively well supported in the vertical but be subject to considerable flex in the horizontal plane.

For these reasons among others I've rejected drawer slides in the past but might reconsider if I found some that function similar to "Redi-slides".