A Hard Case to Crack

Good progress today. Linear rail for gantry drilled and tapped and gantry motor mount made!
I'll start with the motor mount as its very straight forward and need little explaining.
Here is a pic!

Its 6mm thick. I had to put it in the 4 jaw chuck on the lathe to cut the big hole.Drilled the 4 holes to 4.2mm and tapped M5. I've yet to drill the holes to mount on the gantry. I need to get the linear bearing first...

But the big thing today was the supported rail for the gantry.

 I'm going to go into a bit of detail here because

 it was a pain to get this done untill I got the knack!

 (and this might help someone trying the same thing)

In this project I'm using 16mm linear rails. They are case hardened, which means no drilling into the surface.
But...below the surface is normal mild steel! So I can work that easily if I can just get to it!
If your drills or taps touch the hardened steel the will snap.
So follow the steps below and your laughing!

1. Mark your drilling points with a permanent marker (don't bother trying to scribe a mark at this stage).

2. With an angle grinder, grind the spots you've marked. Be careful, try to stay inside your support width, 8mm in my case. The point here is to get the centre of the cut to be through the case hardening.

Here is the first cut

3. Remeasure, scribe and centre punch your drilling points.

 4. Get a tile drill at least 2mm larger that the thread diameter of your tie down bolts. M6 in my case so I'm drilling with an 8mm here. Naturally you want to use lubericant of some type here... an interesting side note, normally these drills are used for tiles and glass and water is the lubericant. But I have a suspition that the water is a coolant not a lubericant.

I noticed that it wasn't untill the oil I was using was pushed out of the drills path did it start cutting properly.

5. Drill with the tile drill untill you are at least 1mm larger than you tap diameter. So I drilled in to 7mm or so!
Now you can go ahead with a nornal tapping drill size as you are throught he case hardening...

 6. Once you've done one hole, go and tap it!
      You see the gap between the tap and the case hardened steel.

 Now scew in a short length of threaded bar. This will help ensure all the other holes are on the same axis!

7. Go ahead and drill the other holes. Tile drill then tapping drill always using the threaded bar as a guide to the alignment.

When you have all that done mark and drill the U channel. It will all line up... and you get:

Lovely.

Good money for scrap metal

Here are some photos of progress!
Below is how the bottom frame will be held together. I am dubious about how good this method can be as there is no triangulation. The Aluminium here is box 50x50x3 and angle 80x80x8

 I'm not sure exactly how long the Y axis will be it is dictated by the length of the belts, plus whatever they are tied to, ie: the gantry.

 This is in no particular order, I'm kind of working on the whole thing at the same time. Its the way this has to happen as far as I can see. Every part has an effect on the other parts. Its messy!
Below is the gantry toothed pulley. 15 3m 24 size. That is to suit 15mm wide belt, 3mm pitch, 24 teeth.(thats a mouthful)

 I was out on a film shoot and I spotted the camera dolly was on round tracks, supported on a U channel, not a solid block. It must be stronger that I guessed. I used solid bar on my last supported rail effort for my CNC router.

 Here is the 1800 3m 15 belt from Polybelt in th US of all things this is dictating the size of my cutting area.

Its probably going to be under 900x900mm

Thats not the end of the world. Its also a floor space issue!

 There is the Y axis motor. Salvaged from an old photocopier, years ago! I drilled out the pully and pushed it on. It was drilled out on the lathe. I'll eventually put a grub screw into it.

 I'm really waiting for the linear bearings to arrive now. I don't want to do any work assuming they will match their description regarding tapped hole positions. C'mon China Post!