Flappy machine - Advise needed please!

[firetrappe]

I had similar problems with corners cutting as curves. I changed from CV mode to 'Exact Stop' mode in Mach3 and it solved the problem. I know there are probably better ways by tuning CV mode etc, but it might be a quick way of proving whether it's mainly a software or hardware issue.

Si.

[routercnc]

Hi Jim,

Glad to hear you are enjoying the machine despite the problems. The rounded corners sound like the software setting already mentioned, but on the subject of unsupported rails - my first CNC machine used 900mm unsupported 20mm rails for the Y axis (it was a 'landscape' machine rather than the more usual 'portrait' machine) and 600mm unsupported 20mm rails on the X axis. The Z axis was around 300mm unsupported round rail.

I paid about £50 for all the rails and bearings (from a colleague) just to have a play with CNC and see if it was just a passing phase. Well the machine did work, but it flexed badly. The cutter was almost dragged through the work (plywood) at a slight angle so feed rates had to be low. However, I was hooked so I sold the mechanical bits on ebay and designed the machine I have now which is much better (although about to upgrade again!).

I remember playing around with temporary supports clamped to the rail at intervals (if the part being cut was small) but this didn't help alot. As Jazz as mentioned I think you might go the same way - trying bits and pieces but not making too much difference. Jonathan's suggestion might work (change bearings for half-bearings and try to support the rear side of the rail), and I had the same idea with my original machine but didn't do it in the end for fear of grinding the toughened surface to be able to drill into the softer core (to tap) and releasing in-built stresses and distorting the rail. I might have been worrying over nothing there - but it would also have made them more difficult to sell on e-bay after use so I didn't pursue.

About 2 years ago I bought a pair of 16mm supported rails around 1300mm long for ~£100 from Chai on LinearMotionBearings2008 (ebay), so this is probably the best sort of upgrade for your £100 and you could use it on your next (!) machine, but the unsupported Y axis will hold you back.

By the way what rails are on your Z axis because this is also part of the chain?

[EddyCurrent]

The term "Mission creep" springs to mind.

Edit: Jim your original 'rough diagram' did not do your machine justice, it's quite a bit better than that.

[cncJim]

The term "Mission creep" springs to mind.

Edit: Jim your original 'rough diagram' did not do your machine justice, it's quite a bit better than that.

There is always mission creep...... :) though in my experience with IT projects the term "mission creep" is usually applied when the requirement gathering/scoping stage has not been fully completed!

Looking back I guess my diagram is a bit lame!