Inside radius of 0.250" rectangular steel tubing?

[slow-poke]

I'm about to mill a couple of blocks that need to fit quite snugly inside a 2"x4" x 0.250" steel rectangular tube. I'm going to write a few lines of gcode to make it easier.

It would be easier yet if I could match the end mill size to the actual inside radius. Lot's of diagrams and charts via Google, I think I likely have cold formed and for t > 6mm they show r = 1.5 x t , so that would be r = 0.375". looks closer to 0.25"

I'm guessing it's actually 1.0 x t, so I could simply use a 1/2" mill?

 

[MrWhoopee]

I have a piece of that tube in the shop if you'd like me to check, but they may vary between manufacturers. If practical, it's probably simpler to chamfer the corners. Don't forget about the weld seam on the inside.

 

[slow-poke]

I have a piece of that tube in the shop if you'd like me to check, but they may vary between manufacturers. If practical, it's probably simpler to chamfer the corners. Don't forget about the weld seam on the inside.

Thanks for the offer, I have the tube here, I think between my eyeball matching of a circle template to the actual radius and that appearing to match the 1.0t formula, I'm going to give that a spin and see what happens.

 

[RJSakowski]

Cut a template out of cardboard to check the fit. You should be able to come in very close to actual.

 

[Aukai]

How will you take out the inside seam from the tubing?

 

[JimDawson]

Sounds like you need to buy a set of radius gauges.

I assume you plan on machining the ID of the tubing and then making a plug to fit? If you are only machining the plug, then it makes no difference what size endmill is used since you are only working on the OD

On a CNC machine I typically use an endmill that is smaller than the radius on the ID, this vastly reduces the load on the endmill in the corner. It allows the endmill to travel around the corner in a smooth arc, rather than just being jammed into the corner.

When fitting plugs for rectangular tubing, I normally make the corner radius a bit large for some extra clearance. If welding the plugs in you can always fill the small gap with weld if needed.

 

[Flyinfool]

Unfortunatly you have to measure what you have. There is no industry spec for the corner radii of rectangular tubing, there is just a range. Each steel mill does their own thing and even that can vary from run to run.

 

[TorontoBuilder]

I'm about to mill a couple of blocks that need to fit quite snugly inside a 2"x4" x 0.250" steel rectangular tube. I'm going to write a few lines of gcode to make it easier.

It would be easier yet if I could match the end mill size to the actual inside radius. Lot's of diagrams and charts via Google, I think I likely have cold formed and for t > 6mm they show r = 1.5 x t , so that would be r = 0.375". looks closer to 0.25"

I'm guessing it's actually 1.0 x t, so I could simply use a 1/2" mill?

I have made many inserts that slip into steel tube. I have always just milled a chamfer on them via eye til it fit and then matched every other piece to match. It is how I make machine rollers

 

[twraska]

I'm about to mill a couple of blocks that need to fit quite snugly inside a 2"x4" x 0.250" steel rectangular tube. I'm going to write a few lines of gcode to make it easier.

It would be easier yet if I could match the end mill size to the actual inside radius. Lot's of diagrams and charts via Google, I think I likely have cold formed and for t > 6mm they show r = 1.5 x t , so that would be r = 0.375". looks closer to 0.25"

I'm guessing it's actually 1.0 x t, so I could simply use a 1/2" mill?

I can assure, each manufacturer has a slightly different radius.