Reduce steel tube diameter by 0.3mm

I am trying to make a DIY CNC machine, using linear rails and the expert advice in the many awesome instructables out there on this topic. 

I hit my first roadblock, and I need some help/advice please...

The 16mm steel tubes I ordered for the sliding rails wouldn't fit in the 16mm linear slide bearings SCS16LUU that I ordered, they are ever so slightly too big. With a lot of force I could get the rail in the bearing, but it wouldn't slide without extreme force - certainly not the smooth sliding motion it's supposed to be! I've probably ruined the bearings by forcing it in, but I'm not worried about that so much right now (I have spare bearings).

I broke out the digital callipers, and the rail diameter measured 16.3mm - that's .3mm more than expected, and more than can fit in the 16.0mm bearings.

So now I need to reduce the steel rails by 0.3mm. I have only hand tools at my disposal, and no experience accurately reducing steel rod diameter. I guess another alternative is increasing the slide bearing diameter, but these are sealed bearing units and difficult to get at.

Does anyone have any ideas ?  Would it be easier to order new steel?

Please let me know any thoughts on this, I'm desperate here. 

Thanks in advance,



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Best option is to order new rails that are designed for this application. Then you'll get a rod that has tight tolerances so a linear bearing will fit over it. Otherwise you will need to find someone with a metal working lathe to turn the diameters down. Alternately you can alter your design a bit to use cheap skate bearings rather than linear bearings.

+1

-max-3 years ago

Can you turn them down on a metal lathe?

iceng -max-3 years ago

That's Extremely Ambitious considering they are meant to be used as tracks for a CNC machine.

I would in fact rather pull them to a thinner diameter than try machining !

srah1 (author) 3 years ago

thank you all for the replies - lots of great ideas, techniques, tools and alternatives mentioned below! Plus a new term for me, brinell - which looking closely I've now noticed on the (non-hardened) tubes as a result of the force I applied. The bearings appear to have won the fight, will see how they fare on the new hardened and solid steel stock it is. I had originally selected tubes, specifically the steel Ikea Grundtal rails - based on previous "experience" with these rails (for hanging mugs under kitchen cupboards), they come with supports in the pack, and the price at £2.50 seemed like a massive bargain to be had. They also gave me an idea - they have a hex nut embedded in the cylindrical ends, which interface with the supports. I am aware of at least one other diy cnc project using these rails, seemingly that maker had better luck than me. I was/am planning to make the business end interchangeable - a Dremel mill, 3D printer and a laser cutter. Now I need to figure out how to incorporate a mini lathe and a cylindrical grinder! Instructable to follow. Now, hopefully I can select three best answers.....

Anything off the shelf will be to a tolerance not of your choosing that is why you got 16.3 mm when you ordered 16 mm.

You can order a new one to a tolerance you want but it will cost you big time and check your bearings they may not be the tolerance you think ether.

The right way to fix the rails it is to surface grind it on a lath to the tolerance you want.

I am assuming you do not have a lath or surface grinder so you can try to surface grind the rails with a drill, a file, and sandpaper, however it is not an accurate method and you will need a high tolerance.

Joe

FYI Taking off the surface of a rod is done with a cylindrical grinder, making a surface flat is done with a surface grinder.

And how is that helpful to srah1other than to point out the proper name for a tool they don't have?

It was FYI. You are using the wrong nomenclature, if you care.

I'm just wondering how that is helpful or good advice to srah1 when they don't have one.

Now I gave them an option on how they could reduce the rail by .3 mm which they were asking for, "You can try to surface grind the rails with a drill, a file, and sandpaper, however it is not an accurate method and you will need a high tolerance."

Now a cylindrical grinder it the tool, surface grinding a cylinder is the action.

I'm just wondering how that is helpful or good advice to srah1 when they don't have one

Do you know what FYI means ? For YOUR information. I made the mistake of thinking you might like to learn something.

FYI I know what FYI means do you and I think it is a rude term that is why I never use it.

I know what nomenclature means also (The rules and conventions of a names creation.) or did you mean onomastics (The study of proper names themselves.) either way it was used incorrectly.

Do you have a suggestion on how to help srah1 or are you just here to dump on everyone else’s answers when you don't have one.

Can you actually read ? I posted

"You'll have to get ground steel stock, not tube. Its a well known
phenomenon, when you're experienced in the ways of the engineering
world."

Keep up.

You still didn't answer their question.

And I have seen hundreds of rails made with tube stock, in truth it depends on the material, stress applied to the material, and the annealing of the tubing as to weather it will do the job or not.

@OP "Would it be easier to order new steel?" (3rd sentence from the end)

To which : "You'll have to get ground steel stock, not tube. Its a well known
phenomenon, when you're experienced in the ways of the engineering
world."

You really aren't keeping up are you ? Solid, Recirculating ball linear bearings (see OP's comment) need precision stock. They really need to be hardened ground stock too, or they will brinell rapidly. Since the OP doesn't have machine access, he's not got much choice but to try and get better stock.

You are still not answering their question.

You'll have to get ground steel stock, not tube. Its a well known phenomenon, when you're experienced in the ways of the engineering world.