Aiph5u
(Aiph5u (not affiliated with Onefinity))
41
Hey Chris,
but the problem here with the riser block is not in the compressibility of the material. The play with which the machine will be bent will be in the linear bearing’s play. What you add by adding a riser block under the X axis, is leverage force, and deflection amount. The CNC machine is a mechanical chain, and force applied to one end will bend the entire system until the other end. One end is the cutting edge of the cutting tool that tries to cut the workpiece, the other end is the workpiece attached to the machine bed with the four machine’s feet attached to this bed. When you drive the cutting edge (one end) through the workpiece (other end), all parts between those ends (milling bit’s cutting edge → milling bit’s shaft → spindle collet → spindle axle with spindle bearings → spindle holder → Z slider bearings → Z assembly → X carriage → X linear bearings → X assembly → X feet → Y carriage → Y linear bearings → Y assembly → Y feet → table top → workpiece clamps → workpiece) will be subject to forces which originate from the cutting edge of the bit meeting a resistant force on the workpiece. The question is now to design this mechanical chain to avoid weak spots. Between different chain links, there act leverage forces, which have always one effect: To make a resulting force bigger or smaller in relation to the acting force.
Usually you want that your milling motor not to be bent away from the ideal cutting position by the mechanical load of the cutting process, so your goal is to have a machine whose mechanical chain is stiff and is not bent.
Therefore any engineer will tell you
if you want to make a machine like the Onefinity higher in relation to the machine bed, you would rather put a riser under each Y axis than under the feet of X axis, and
you would avoid using small riser blocks, but use wider parts instead.
if you nevertheless want to put the Onefinity’s feet on a block that is only as small as the foot’s footprint, better choose the strongest material.
But the play that you introduce with the risers as described in the thread earlier will not consist of the compression of the riser itself. The play will be always be in the linear bearings, and increasing the length of the lever (that consists of the entire X assembly height) will make the effect of any bending bigger (and the danger of chatter) and of course increase the linear bearing’s wear.
So if you’d ask me, how would I make a Onefinity one or two inches higher than the machine bed (=here a table top)? I would anser: I would not put risers under the X feet, but under the two Y rails, with a part that goes all the way through from front foot to rear foot, one on each side, and I would make it of a 4" wide, possibly 1-2" high, steel extrusion profile with 1.5 or 2 mm wall thickness.
oversized, that’s what I meant with 2.) above
Did you do that on Y feet?
3 Likes
Aiph5u
(Aiph5u (not affiliated with Onefinity))
42
Yes, but still it is a big difference if this small tire’s surface is on a little cube of road material, or on a larger road surface.
I agree, that’s why i was speaking of the higher center of gravity.
And yes i did put it on the y feet.
Putting pieces of plywood on the y would have resulted in the same thing as raising the x except i also have clearance where the x blocks are because it’s like 1/8" on the foreman, but without compromising the CG at the x
Aiph5u
(Aiph5u (not affiliated with Onefinity))
44
My plan is not to use a table top at all, but to weld a U-shaped base from steel profiles that holds each Y axis at its sides and has a space in between for things like rotary axis or higher workpieces, and a system of height-adjustable wasteboard/machine beds.
The foreman has a negative clearance where the x mounts to the y because theyre lower than the feet. I guess maybe it’s called the linear bearing block…
To compensate they added like 1/4" risers for the y feet that are needed on the foreman, unless you use the qcw. Even with these risers, there’s only like 1/8", so i added 3/4" scrap plywood giving me room for a towel for when i have to oil it up.
We’ll call stock configuration orgin 0
Raising the X 1" will raise the Center of Gravity 1" and your adding 2 more points of failure (per side)(the point that attached the the Y block, and the point that connected to the X block) with the extra 1". Its like putting on platform shoes. You won’t be able to run in them like you would without. (Look at Ford on Firestone in the 90s. Trucks and suvs were involved in single vehicle accidents because they rolled over… there was also a part of something being out of manufactures specs which is also relevant)
But if you raise the Y 1", your X will also raise an inch from orgin 0 since the z clearance is dependent on X height which is dependent on Ys height. But when doing that, your not Raising the center of gravity (your just changing the machines height), so it’s like running on a beam but your still the same height above orgin 0 as the platform shoes. Same result, less work, less time, and less risk.
It never occurred to me to raise X here and it didn’t occur to me that’s what he did till after our back n forth started, because that doesn’t sound like a good idea to me in the first place, therefore i didn’t even consider it as an option.
Same with if i wanted to increase clearance on my shapeoko3, i wouldn’t raise the x either, i would raise the y’s (pretty sure there was a bolt on option to do that in the case of my SO)
Don’t mind the clutter and disorganization, this was early stages of figuring it out. I think i took the pic to send to my dad to show him i (finally) got it in.
Aiph5u
(Aiph5u (not affiliated with Onefinity))
48
Hey Chris,
Ah okay. Thanks for the explanation. You are right, I remember I realized it when unpacking the X-50 axis of my Journeyman. This is also the reason why the foot of 50 mm rail is floating above ground in this image here:
Aiph5u
(Aiph5u (not affiliated with Onefinity))
51
Hey Chris,
thanks for the image!
In fact this is the correct solution, as making a higher foot block instead would have unnecessarily added to the overall X height when used as X axis.
PS: I see they are also mentioned in the Elite Manual page 19:
Yep. There is no “well maybe i don’t have to”… well you have to do something because like i said there’s negative clearance from the linear block to foot. I’m assuming the qcw accounts for that by having the foot mount higher than the top of the table or nothing in between
As for the manual. It’s got a lot of good information, but it’s not the Bible, refer to the “power button” in the other thread where when something was described/pictured, and therefore planned around how it was described/pictured but on delivery it wasn’t.
That’s the only instance i can think of because that threw such a big wrench in my plans and forced me to adjust plans on the fly. So that little thing turned out to be a bigger thing, and it’s actually an anecdote i use with my contractor when he comes to me with shop building changes. I planned my shop over the course of months (at least 4-5 and another 2-3 mo to find a contractor who could do it for the amount i have) and i don’t recall why i did every little thing i did, but i did it for a reason.
Where did you get the riser blocks? I am in the process of assembling my pro foreman and noticed the y rails balancing on the bearing blocks as well. I don’t see any riser blocks anywhere yet.
RowdyRoman
(Peter Romano (Official 3rd Party Accessories))
54
Hey I make riser blocks for the x rail. Here is the link
I can make a smaller size for the y rails if you guys need just email me at rowdyromanfire@gmail.com
Thanks for the reply brother, but I was specifically referring to the riser blocks needed for the Foreman (setup without qcw). During setup riser blocks under the y rails are required because the bearing blocks sit on the table otherwise with negative clearance for the feet.
