Here we go again . . . MK4

[routercnc]

This lot arrived recently.

2off - RHS for the raised X axis sides - seems pretty square and reasonably straight




2off - 80x40x4 RHS for the gantry beams

1off 30x5 flat bar to reinforce the gantry beams where the rails will sit


2off ballnut mounting blocks (~£9 each)


And 4off 16mm open bearings to double up on the Y axis to make 4 per side (no photo)

Also, got a bit of time this week end to nearly finish the X axis motor mount / belt tensioning plate:

Laying it out:


First pocket:


More cutouts and slots:


Holes spotted, top skimmed, and profile roughed and finished:


Bought a new 6mm 2 flute 45deg helix (for aluminium) carbide from 'cncpoorboy' on ebay (for about £9) recently and just tried it out.
http://www.ebay.co.uk/itm/2014350347...%3AMEBIDX%3AIT

Very impressed with the finish:



Some work on the drill press:



Need to skim one side and tap the M5 holes for the stepper, then its another one done.

In case you were wondering the slot will hold the head of 2off M8 bolts to stop them rotating whilst allowing it to slide in the slot. On the other side will be a spacer and a bearing guide to tension the belt.

[routercnc]

Tiny bit of progress. X axis motor mount / belt tensioner plate finished.


Here is a trial fit of an M8 bolt head in the slot (final part will use an M8 nut):


Also started making one of the bits on the gantry. I snapped a cutter on final the 20mm pass ! Always the worst bit right at the bottom of a deep slot when the chips can't get out. It welded up and I didn't stop it in time.


Luckily I had a spare so finished the cut. Setting up for the holes in the edges.

[Clive S]

Coming along nicely where did you get that vise?

[routercnc]

Hi Clive
Thanks for the encouragement! If I multiplied time taken per piece by number of pieces to make I might get disheartened. So I'm trying not to think about it.
Vice was from Arceuro. It was about £35 and is surprisingly accurate (a DTI along the fixed jaw barely moves) and the base is fairly parallel to the jaw runner surface (therefore workpiece is fairly parallel to bed)
But after first use the thread got swarf on it which went into the nut and it is very hard to turn. I can't get it apart to clean it out so if you get one put a cover on the thread first. It's actually a drill press vice but is working ok for my gentle machining
To be honest I am going to replace it with a precision vice as one of the future jobs needs to be more accurate than this and I'm fed up trying to tighten the screw. Arceuro make some nice ones with ground surfaces all over and antilift jaws. They are also quite low in height which is good. if I buy one and like it I may get another as a pair of vices can be really useful

[routercnc]

It's been a while since I last posted and I'll explain why in a moment. I've made a matching pair to the last part, with a bit of finishing off to do:



Reason for the delay is that I've noticed for some time now that even mild cuts are often generating lots of chatter. I think it has been getting slowly worse, and feeling the Z axis around the rails and bearings there is some relative vibration between rail and bearing, especially at the top left bearing, when the chatter occurs.

Problem is that the chatter can quickly lead to welding, and with so many parts to make for the new machine it was time to check things out. For info I have been running these 15mm linear profile rails (classed as 15mm minature) for about 5 years on 3 successive machines, and that they were bought as used from 'fa-systems'.

I stripped the Z axis down and found significant fretting on the rail, especially around the top left bearing:


Luckily I had a second set of 15mm rails (new) that I'd ordered for the Z axis on the new mk4 machine. However, the hole spacing was 5mm further apart on the bearing carriages. I ended up drilling another set of 4 holes rather than 2 extra holes because the holes would have been too close to the existing ones:


I took the opportunity to drill some access holes in the outer plate so I could assemble the Z axis as a unit, and then bolt it on to the Y axis. It's easier to get everything lined up off the machine rather than trying to assemble it bit by bit on the machine:


I then set the first rail off a side datum, and then clocked in the other rail:


Then assembled the Z axis onto the machine:


I trial cut revealed a much improved machine. A 1mm DOC at 900mm/min 12,000rpm 6mm 2f carbide was fine with no chatter.


So is there a moral to this story? Well my rails were used when I bought them so it's had to be sure but for the occasional poster on here who asks about rail size then I will always recommend 20mm over 15mm.

Back to the new machine. As originally drawn it had 4off 15mm rails around a box Z. Although these are used as 2 pairs loaded against each other I did not feel confident in continuing with 15mm rails all round. Luckily I had left space in the Y axis to upgrade rails or spindle size. So it was a simple matter to add pockets and fit in 20mm rails. I've ordered 20mm rails from Fred, and will use the new 15mm rails just as auxiliaries away from the spindle where the loads are lower.

[routercnc]

Whilst cutting another new part I used 'feedhold' to stop the machine just to check something was not going to collide. Then I hit 'start' but instead of continuing on a +X direction to the end of the cut the machine moved in +Y. It was about 8mm into a profile cut so snapped the cutter.

Luckily this was in the scrap part of the material so no harm done. I changed the bit, homed, ran it all again. Later on in the same profile cut (in the -X direction this time) it was almost to the bottom when I pressed 'feedhold' again to check one of the clamps was not going to get machined through. When I hit 'start' is again went in the +Y direction. Luckily I had my hand over the e-stop but it still took a chunk out of the part!

I've never had this happen before and haven't changed anything in software, just the Z axis bearing change. Any ideas?

[Clive S]

Did you by any chance stop it in a canned cycle I have a feeling that it happened to me once.