Upgrading 9mm belts to 15mm

[LiamN (Liam Newcombe)]

That’s a well described set of goals.

I had some similar goals when I did the rail and belt upgrade to the X axis of my SO3 XXL with HDZ. I went through and looked for all the sources of deflection and backlash in order to understand what the relative benefits of fixing different elements would be

Backlash, Deflection and Vibration

Firstly, Thanks to @Julien @gmack and @spargeltarzan for their comments and assistance, quite a few poor assumptions of mine were corrected during the process of this investigation and write-up. Obviously the remaining mistakes are mine alone. Here’s all the content below as video on YouTube, some of these things are easier to explain with the video, it’s broken up into 3 videos A zip file with the machine deflection models, this text as a single PDF and a word doc with the maths I used fo…

One thing to note is that on an XL or XXL you have inherently more deflection than on the regular SO3. The small machine has really rigid beams for it’s size, the XL and XXL sizes are much more flexy (like an order of magnitude more) due to length so you will not achieve the same sort of performance the likes of Dan and Vince got on their regular sized SO3s. Same applies to the baseboard but you can (and should) reinforce that.

@AndyC

@LiamN Liam, I am machining more Aluminium now than before, and I hit surprisingly low MRR limits before juddering sets in.
An example, Alu 6061, 6mm 3-flute DLC fast helix mill, 0.6mm DOC, 3.6mm WOC, 13,500 RPM and Feed 1,900 mm/min, spray mist alcohol, Conventional Cut, Adaptive Roughing F360.

That’s actually pretty good, as Nick says, a single flute can be the tool of choice, I’ve had good results with DLC coated single flutes. I also learned a lot about the forces on the cutter and how they interacted with my machine from Spargeltarzan and his app Millalyzer.

@AndyC

Keeping chip-load within sensible limits for the end mill means backing off significantly on particularly DOC otherwise a definite juddering sets in on Y axis cuts (front to back on machine) - these settings ‘just about’ keep the juddering away. Impact on cut surface is vertical ‘ribs’ showing the oscillation as much as 0.2mm deep, impact on my nerves knowing something is unhappy about 10 meters deep.

Observations on cause and effect of the juddering;

• Climb cutting is significantly worse than Conventional
• DOC at 0.6mm is the next most sensitive parameter, all other things constant
• Trying non-adaptive tool paths didn’t make any noticeable difference vs adaptive, the same sort of limits seem to be the maximum I can run at
• Increasing/Decreasing Feed by ±10% then ±20% didn’t find a sweet spot, just increased or decreased the intensity of the juddering. No amount of reduction seemed to stop it
• I haven’t tried increasing/decreasing spindle RPM to see if a sensitivity arises from that
• Stock clamping is to the aluminium T-slots, not to the MDF spoil board, to avoid lifting/moving the MDF. I have self-made T-Track bolted to and through the base-board on 200mm centres
• HDZ and water-cooled 1.5KW VFD spindle - the mass of all this may be a factor, but I can’t determine that as yet

Yep, all consistent with what I found. It’s not a simple single resonance, it’s a whole bunch of undamped deflection modes all over the machine from the Z nod around the V wheels to X beam flex, deflections in all three DoF in the Y rail V wheels, the bed trampolining around etc.

I believe a major part of the vibration is positive feedback between cutting forces and spindle nodding which is much worse at higher DoC, thus the WoC preference many users have determined.

@AndyC

• There is no discernible movement on the spindle shaft itself in any direction
• All belts checked and tensioned ‘on the tight side’ of right, recently replaced all Vee-Wheels with a service kit, although none were damaged on inspection. I also have the high precision eccentric cam adjusters - all Vee-Wheels adjusted to ‘only just able to spin by hand’ tightness. I would argue these may all be a little over-tight if anything

Be careful with belt tension, the stepper shafts are already close to their working limits at the recommended tensions and there is no reduction in deflection or backlash through increasing belt tension above the minimum required to avoid a slack side under stepper power. You’ll just wear out motor shafts, V wheels and belts faster for no benefit.

@AndyC

• Dial gauge onto the spindle collet shows 0,2mm under-tuck (bottom pushes away) and 0,4mm forward-tuck (bottom comes towards) when pulling and pressing ‘hard’ against the spindle - which shows some flex happening. This must Vee-Wheel play, Beam twist or dual-Y stepper belt stretch
  -Repeated with the dial gauge against the Alu Beam instead of the spindle, 0,2mm under-tuck and 0,3mm forward-tuck - which suggests the majority relates to the beam rather than the Z-axis being ‘wobbly’ on the beam. I ensured I was not levering against the bed when pushing/pulling, to remove the possibility of bed flex. What I haven’t yet measured is whether this movement is belt/stepper related (the beam is linearly moving aft or forward, not twisting, or the vee-wheels are ‘rocking’ somehow) - I intend doing this right up against each side carrier plate
• I also haven’t yet measured side-to-side rocking of the Z-axis

Yep, several of the key deflection modes, you might enjoy the deflection tables in my long post linked above

If you really want to chew Aluminium I’d suggest selling the S03 and buying a pro as your starting point. If you like to upgrade and mess with your machine then by all means. If so I’d suggest the order of benefit is;

1. Support the baseboard properly, keep it rigid and square, it’s not really up to the job on it’s own
2. Linear rails on the X axis to control the HDZ
3. Linear rails on the Y axes
4. Mess with the belts, the parts from the later machines are probably the best way to do this, I found 15mm width 20T GT2 pulleys to be tricky to find

HTH