View Full Version : Effect of drilling hardened linear rails?

21-08-2010, 09:51 PM
Does anyone know if drilling holes in a hardened unsupported linear round rail would lead to distortion due to residual stresses in the material?

Are hardened rails stress relieved at the end of the process?

This is with a view to converting them to supported rails. I'm not looking to do this, but it was part of a discussion on another post, and it would be useful to know.


21-08-2010, 10:12 PM
I'm very interested in this topic. Ideally I would like to drill and tap some M6 holes in the rails and use them to add support...

22-08-2010, 01:23 AM
I think the main problem is drilling thro the hardened surface, lots of heat etc. and possible distortion. If it was me I would slow grind the surface with water or oil and then slowly drill with lots of coolant.

its only the heat that will bugger them up :smile:

Huumm didnt read the other post on stress relief, could be a problem, needs somone to try it....... how did you get on john?????

22-08-2010, 09:36 AM
Hi Ross,

I think drilling the hole would be fairly straightforward, and I would do somthing similar to what you suggest - make up fore/aft sliding grinding jig to grind a flat spot. This gets through the hard layer, and provides a nice flat area to drill, counterbore, tap, whatever.

My concern is the act of drilling the hole, and whether there are any residual stresses in the bar which then give rise to distortion. These bars are precision ground to be straight and round. How much would this operation upset that? If they are not stress relieved (heat to ~1200F then cool very slowly I think is one method) then there is a risk.

Jonathan hasn't actually tried it by the way.

22-08-2010, 10:22 AM
Why does it have to be drilled?if we make a block like the pic below out of ally? fixittothe base/bed then place/clamp the rail on to this temporarily to get the precise height for the end support rail mounts.


22-08-2010, 10:33 AM
Because george, that will on provide support in one direction... when used in a Z-axis the forces are both into and away from the support...

personally I'd not both trying to drill it, whats wrong with using proper pre-drilled supported rail?

22-08-2010, 11:13 AM
I can't find pre drilled rail cheaply. Using proper supported rail is more expensive than what we're discussing.

With regards to drilling it I was thinking just use a carbide drill and *plenty* of cutting fluid/coolant. Carbide drills are cheap enough on eBay.

Peter Griffin
22-08-2010, 01:42 PM
What about spark eroding the C/bored holes in the rail and tapping the support.

30-08-2010, 09:20 AM
These bods do the rail pre drilled and mounted rail quite cheap....


30-08-2010, 12:26 PM

Just as thought price up the rail you need and get a quote from a local engineering works to drill the holes for you? Factor in buying a box of drills (being that they are all the same size). You may be surprised that it could be cheaper than you think? I got a quote last year to have thirty holes drilled into some plate at odd angles (lots of machine set up time) for 30. They may look at the job as being just some holes drilled in a straight line?

Worth a punt?

30-08-2010, 12:28 PM
Yes, that could be worthwhile for my X-axis since it's much longer etc. I'll look into it at some point - need to find somewhere nearby that does that sort of thing.