Sure,
I had my frame @ 8.5 deg or so, or on the 8deg side of 8.5deg, and with my initial (squarish) sled I had the following problems:
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i initially had the suggested 2x4 riser for the vertical pantograph linkage, I wasn’t happy with the lateral strength of my construction both of the riser to the sled and the riser distances (this was before the vertical pantograph included a vertical spacing bar). The chains were ~5" above the sled and that made spacing the chains out as parallel to the workspace a little more difficult to measure and get perfect.
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my weight placement on the sled was more ‘straight down’ than ‘opposing each chain’, more spread out. This was partially because of my square sled and reluctance to mess with the weights as they seemed to work ok, but I hadn’t yet solved a quick connect of the chains to the linkage kit.
I ended up making two 1/2 links and getting some cotter pins that fit everything well, it’s still awkward with the sled weight (a sled balancing mount will be in my 1st set of new builds sometime this week)
I purchased a T made of aluminum extrusion (4" x 7") to be able to precisely mount the vertical pantograph kit, adjust it easily and get more precision than 2 lag bolts in wood.
Mounting this on the ‘squared’ sled left very little force holding the sled to the work surface, but it was mostly there, and i was able to make my initial cuts, as documented above.
I then cut the sled with 3 different Fusion360 programmed maneuvers, 1 drilling operation, 1 pocketing operation to countersink 1.25" washers for the weights and vertical panto, and a contour for the central hole and sled profile.
It was during these drilling and pocket ops that I hit upon some Z-axis slop and the current 2-D + Z-axis movement restrictions.
problems encountered in my sled cut are documented in my thread about 3 axis movement. namely that drilling the z-axis alone relies only on the sled pressure on the workpiece, which was already low in my squared (v1) sled.
This is where i became more conscious of the true frame angle and after reading up on the forums realized my 8deg angle was def a little too low for others (@Gero for example) as well.
Also, while cutting the new sled, it was obvious that the router and X-Y movement were pretty spot on using 4mm cutting depth, it was steady and true and the router wasn’t complaining. I put a little more pressure on the sled by hand and it cut like a champ, and looked and sounded like it would have no problem with a little more speed and a little more depth. (see my observations in How fast does everyone cut? )
Unfortunately, enough slop persists in the router’s Z screw that I ended up not raising the bit high enough in a couple of traverses and some plunges weren’t ideal.
I’ll be upgrading to a ball screw for the Z-axis asap, and ditching the router base I imagine completely.
anyway, today i was able to change the frame angle to 11-11.5 (will micro adjust it tomorrow if needed) and after assembling and reattaching my new standard 18" round sled, the whole assembly was immediately more solid, plenty of pressure on the work surface now I think.
I haven’t weighed my sled yet but I have (5lbs of lead +2lbs of steel =) 7lbs x2 as weights, maybe another 2lbs for the extrusion and pantograph. My sled is 3/4" home depot cabinet birtch ply. its on the heavy side for what it is, I think, but not absurdly so.
the router is 10lbs? so my total sled is (14+2+10+4) 30lbs? give or take.
I ran out of time this afternoon and had to hit up a birthday dinner, so I’ll have more tomorrow, and will be cutting 2 new sleds for the ring and to replace the current sled to remove the transversal gouges encountered on Friday, even though it’s probably not entirely necessary.
I’ll get some video and picts to show how I’m adjusting the Strut frame and how its cutting now.
The biggest difference needed now (as observed while holding my v1 sled flat against the workpiece) is coordinated 3 axis movement to minimize the start-stop conditions from zero load (of sled and bit) to 100% load (of sled and bit) after a z-axis plunge.
If a continuous 3 axis motion is programmed there should be no need for a part contour to stop after ramping into the surface until hitting a tab operation, where a little over/undershoot would be easily fixable by changing the size of the tab to remove the effects while maintaining a strong enough tab.
more as I have it.
cheers,
