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Mill Stand Design - Static Stress

PeterT

Ultra Member
Premium Member
I see. I didn't realize what was front vs side on your sketch. From a stability standpoint it means you will have considerably more lateral (left-right) & less (fore-aft) stability.
The RF-45 sheet metal periphery doesn't extend out much in any direction, arguably less in depth but I cant recall the details.
I cant think of too many times I ever had to get in behind the mill. There was nothing there except a panel to look at inside of column. If you have or plan to install DRO that might be a reason to get elbow room, but your castors/plan looks like it will accommodate just fine.
 

Dabbler

(John)
When moving a top-heavy item like a mill I try to increase it's footprint, and then use exactly 3 moving skates. 3 skates may feel less stable than four, but in even slightly uneven floors one skate always lets go, leaving the load much more unstable.

Even when I move a full sized mill with a pallet jack I set it on moving bars and then on the pallet jack. the moving bars have a threaded hole on each end where a ready rod goes through. I lower the ready rod to about 1/8" above the floor, so if any tipping occurs the ready rod makes contact with the floor. You can easily see it and feel it, and stop.

@Eyecon I really like your design
 

Susquatch

Ultra Member
Moderator
Premium Member
Are you saying to make the legs tapered to the outside? kind of like how smallish bandsaw stands are constructed?

Not really. More like a modified bottom with braces.

Bandsaw stands of that size and weight would require cross braces


I droped that idea very quickly when I got a quote for the price of the plate :D for now I'm putting 3/4" MDF or plywood and eventually will be making a sheet metal tray for chips and coolant. This is why I added the two bars basically to drill holes through and attach the mill base through them

So much for that. When I first heard solid plate I figured money was no issue. Since it's history now, you should consider a modified mounting with braces extending from further down the legs to the base mounting points or just beefing up the angle iron section.

To be honest, your stress results convey the idea of gross deformations that will never be seen in reality. They look like huge deformations. In reality you are probably only going to see 50 thou or so depending on the span, the cross section of the material, the moment of area, and the weight.

It's not that the images are not useful, just that they are not at all representative of actual bending.

If you make your stand however you like dimensionally, and then add struts from the actual mounting points for the mill bolts down to a point halfway down the legs, creating corner triangles, the thing will be a brick poop house and even your stress result will look pretty stable.

It's so easy to over design such a stand an worry too much about the performance. Especially when a little experience with structures can make the design perform incredibly well.

Another reasonable approach in the absence of structures experience is trial and error. Just build it, measure the deformation, make some improvements if needed, and then get to making stuff with your mill.
 

TorontoBuilder

Ultra Member
View attachment 28539
I made these for my emco. Theres a hockey puck inside each one. Piece of 3.5" ish pipe bored to fit the puck tightly, capped with 5/8" plate, tapered a bit, drilled and tapped the plate 3/4" so i could thread in a piece of 3/4" all-thread with a jam nut. Tightened up the jamb nut to lock the all-thread and welded the jamb nut to the plate. The puck is what they sit on and extends past the tube maybe 0.100" or so. Took a couple hours to make all 4 and cost maybe 20 bucks.
I did similar, but went thru an evolution, hockey pucks and large belleville washers... then cones with whole hock puck inserts, then lower profile cones with pucks sliced in 1/4... far less boring
 

Tecnico

(Dave)
As I continue fine tuning this design, I wonder if anyone knows where I can source machine leveling feet? The stuff I can find on Amazon seems very flimsy. I initially wanted leveling casters but now that I got a 1 ton shop crane I just want to be able to level the stand as my garage floor is heavily sloped.

You can make simple/low cost leveling feet by capping the bottoms of your leg tubes with 1/4" plate and tapping for a suitable bolt, say 1/2-13. Roll the table into place on your casters and when you're where you want to be just lower the bolt heads to the floor and jack up off the casters. A lock nut will keep the adjustment. You can level and compensate for uneven floors all at once. You could put cut down hockey pucks under the bolts if you want some isolation or to not mar the floor. Two fixed castors make for easier manhandling as @Susquatch has said.

In my "Intro" thread (Tecnico's intro thread) I put a few pictures of the stand I did for my lathe with PA casters and corner bolts. For reference it is 1-1/2 x .100 material.

If I read your model correctly you plan to bolt the top and bottom horizontal tubes to the leg weldments via gusset plates. You should really weld that joint or change the design of the bolted joint because the through bolts you have will only be able to sustain as much pre-load as it takes to bend (crush) the wall of the tubing. That's nowhere near the 80% yield torque you mention and not enough to keep the joint from hinging at the bolts unless you're using cross bracing on the long sides of the stand. Think of the bolts as essentially pinned joints unless you're clamping through solid material in the joint.

Hope we're not overloading with all this "helpful" advice coming from every direction!;) In the end you're going to pick what works for you out of all this and it'll work out fine.

D:cool:
 

Eyecon

Active Member
the through bolts you have will only be able to sustain as much pre-load as it takes to bend (crush) the wall of the tubing.
I plan to use short sections of 1/8 DOM tubing as I usually do with bolted tubing. However I am considering just welding the whole thing together to simplify and speed up the build…not even sure I’ll use the gusset plates in this case. I know they’ll add rigidity but going by this build:
I don’t think I’ll have any issues. I’ll have similar angle pieces to act as braces and shelves for the tool chest/drawer unit.
 

Tecnico

(Dave)
I plan to use short sections of 1/8 DOM tubing as I usually do with bolted tubing.

I wondered if that was what you had in mind, I probably should have mentioned it. I'd weld it like you're considering for the same reasons.
Like I said, it's going to work out in the end and we're all going to think we helped make it better.:rolleyes:

D:cool:
 

PeterT

Ultra Member
Premium Member
Is it an optical illusion or are both your L&R bolt holes both to the left side of cross members (vs centered?)
From personal experience, you might want to confirm the physical hole spacing in the casting vs what they may publish in the docs & allow yourself a bit of dimensional wiggle room.
 

Eyecon

Active Member
Is it an optical illusion or are both your L&R bolt holes both to the left side of cross members (vs centered?)
From personal experience, you might want to confirm the physical hole spacing in the casting vs what they may publish in the docs & allow yourself a bit of dimensional wiggle room.
Nice catch! I updated the width to accommodate the tool chest but didn’t update the joint offsets for reflect that so they are actually offset but they are not supposed to be. To your point, I’m waiting for the machine to arrive to double check all dimensions before even ordering stock.
 

Susquatch

Ultra Member
Moderator
Premium Member
Nice catch! I updated the width to accommodate the tool chest but didn’t update the joint offsets for reflect that so they are actually offset but they are not supposed to be. To your point, I’m waiting for the machine to arrive to double check all dimensions before even ordering stock.

Now that I see what those cross braces are for, they are ok. But given how far they are from the legs, you should at least plan on way to increase the moment of area of the two main beams or to install struts afterward if there is too much bowing for your liking.

Are those wheels as close to the edge as they can go?

When does the machine arrive?
 

ducdon

Super User
Premium Member
Engineering aside. Machine tools like a base that includes materials that absorb vibration. Thick wood top, cast iron, etc. I moved my SB 9 inch lathe from a wooden bench with a 2 1/2 inch thick wood top to a steel stand. Bad move! More noise and more chatter.
 
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StevSmar

(Steven)
Premium Member
…In industry we used an iterative approach to stress and function analysis. First you model the part and do your analysis with best guesses based mostly on experience. Then you make a prototype and test it. Then you change the model parameters till the model gets the same results as the real world tests. Then more model changes to get closer to the Design goals, then more testing, and more modelling revisions. At some point you have to go with it….
When I was in University I became enamoured with the thought of Computational Fluid Dynamics revealing all, I must have spoken to a professor about it and he asked me if I knew what CFD actually stood for, in his opinion it wasn’t Computational Fluid Dynamics, it was “Can’t F&%king Decide” (what the results meant…)
 
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