Thread: BigG CNC

It is starting to look like a CNC machine now. The afternoon was spent mounting and levelling the base frame to the cabinet.
I use a machinists level to get the components to within 0.02mm also checking diagonals, etc then I pin the steel with roll pins to make sure it doesn't move.

I fitted the linear rails on the X axis today and noticed that one round rail was lifting on one end slightly when pressure was applied.

Simple fix take the rails off and tighten the cap screws that hold the rail to the aluminum mount. All the cap screws were loose but on the end that was causing trouble the cap screw was stripped. Replaced the cap screw but the new one stripped as well.

Ran a tap through to clean up the thread and broke the tap in the hole which was not a good thing to do.

Ok I'll drill and tap a hole next to the broken tap and start from fresh. I have some cobalt drills and even those only just marked the rail as the rail is super hard. No wonder I broke a tap in there.

It is not looking good so back to the broken tap and try to remove it and see what the problem is. About an hour wasted breaking up the tap with a centre punch and prising out the pieces. I have a mate with an EDM machine and was nearly going to make the trip to have the tap removed when I struck gold and finally got the last piece out. I broke the end off a centre punch during this event.

Ok a closer look showed the thread was good from what I could see. I tried anoither cap screw and noticed that it went in fine for about 6mm then tightend up. Screwed it down some more and it stripped. Pulled all the cap screws in the rail and noticed on the end of each it was stripped. This was the clue I needed and obviously the cap screws were too long and threading into the taper of the tap that made the thread. Simple fix was to replace all the cap screws with slightly shorter ones.

I wanted to share this as it was a relief to find the problem and to let others know to check the rails before mounting for the same problem. The rail needs to be firmly fixed to the aluminum mounting otherwise you will get unexpected results with your machine.

Oh yeah don't try to re-tap the thread.

Sorry about the long post but it makes a good story and it might save somebody else with the same problem.

More progress
Gantry bearing plates and sides were cut on Morphy at 1380mm/min and 0.5 DOC with a 1/4 inch two flute carbide cutter.
You can't take the woodworker out of a machinist - note the housing joint in the gantry sides.

BTW ally plate is free these days - you only pay for the scratches they put in when handling it - this plate was expensive.

Getting closer......

A step backwards this week. I found there was too much racking (twisting) across the gantry and decided to fit an additional plate over the gantry ends.
Rather than try to match to the plate I came in 10mm and only extended out on the edges were it needed additional support. I think this was a better solution as it looks like it was designed from the start and it does not make the edges look too fat.

Result was what I was after and even without stitching around the perimeter or fitting the under plate it has stiffened the gantry no end. I did loose two days but it is easier to do it now rather than when the machine is running.

Photo shows what I have done. Note the pencil attached to Z axis and this is how I square the machine. I scribe a line in X and Y directions then check it with a roofing square. My square is spot on but I do run a line backwards and flip the square as a double check.

Looking good rod, it gives the machine a bit more character the way you have done it, was the original plate 10mm?

Hi Chris,
Yes original plate was 10mm which was a bit silly of me to think it would be ok. Trying to keep the cost down but it ended up costing more.

Moving forward .......

Table and spindle fitted and a few other bits. Laser crosshair, limit switch mounts then cable it up and see if it runs.

Looking great!
How thick is your alloy bed? Will you mount t-slot on top or MDF?

Cheers
Brian

Hi Brian,

Ally plate is 8mm and has 72 fixings back to the steel frame. 36 are cap screws threaded into the steel and 15mm away is a grub screw threaded into the ally plate. This allows for levelling the plate by a push/pull method.

Hard to see it but there is T track running down both edges of the ally plate. I make steel clamps to go across the table. A 6mm MDF spoilboard goes on top of the table to stop any damage to the ally plate with through cuts or oopsies.

Thanks Rod,

I can see the T track now. Wow Big G has everything.

You have given me some ideas for tweaking the bed level on my machine.
I am now thinking of using 10mm square bar bolted to the side supports under the angle for the bed with grub screws to adjust each of the bed supports.
I am just at the stage checking the bed level against the side rails before mounting the gantry. I still need to disassemble for painting so good time to add any extras.

Cheers
Brian

Hi Brain,
What I do from here is attach a dial gauge to the Z axis and adjust each point to zero with the gauge. Doesn't guarantee there isn't a twist in the machine but it does give you an even bed.

Hi Rod,

Did you get the laser crosshair from Dealextreme? It looks like they no longer ship them to Australia which is disappointing.

Got them from here