Higher End Large Format Router Mill Project

[jsage]

Greetings Folks,

I have put in my time reviewing different projects, resources on this fine site. Decided if I am going to go through the process I might as well share my success and or failure with anyone interested.

I just finished an interesting pdf posted on the site. A deterministic process for evaluating design option towards a specific outcome. It's an MIT Doctoral thesis that seemed to fall under philosophy. I guess at MIT the technical component is assumed. Of value I think it provided a good structure/methodology for developing a CNC machine. Kudos to the poster and the writer. Coverage of beams, solids, tubing, finite element analysis, pugh charts, damping were interesting.

Thanks to Joe and Mr. Steele for sharing their projects.

One thing I notice that there is an expectation by some to have everything figured out in the beginning. I find that problematic since in many design cycles I have seen The process is iterative and a change in one feature changes the others.

Anyhow enough intro.

The goal:

Universal Platform- the capability to work with a variety materials and project sizes within reason. Expandability within reason, additional axes, fabrication methods.

Honest 8' x 4 x 2?

base welded steel tubing (on hand) concrete dampened, torsional box upper frame with basin, polymeric concrete work surface.

ball screw, linear slides (fabricated where possible) determine most affordable compromise

capabilities: standard woodworking, rough lumber milling, green concrete, aluminum, mild steel, FRP Sectional mold prototyping.

Target Initial investment for base platform $2,000

[Madclicker]

You lost me at $2000. That's an unrealistic number for the machine you described.

[jsage]

I can see your point. To some degree it is based on materials on hand. A better way might be saying my incremental investment. I'd say I have 90% of the structural components which leaves ball screws, and drive systems. I'm looking to fabricate the initial linear slides in aluminum.

It may be unrealistic but it is a starting point. I probably have a couple hundred feet of steel pipe (schedule 40 type) mig welder 20 inch band saw aluminum capable. 2 1/2 hp router. Pentium desktop system (using laptops).

So the goal is use materials at hand with carefully chosen bargains.

The X will be driven by a single screw below the working area in its own torsion box.

[jsage]

The major goal here is rigidity.

Nixed: The four pipe construction is intended to approximate the mechanical characteristics of a 6 inch square tube.

Nixed: The four slide design on the long axis is designed to give three point support and allow stability for a long z axis.

By committee ; ) it was decided that the pipe method was two challenging to maintain true and square dimension, beside being a lot of work. The value of the lower slides and ballscrew placement was similarly thrown out for the conventional dual screw method.

First images include revision to 4" frame 2" gantry. 4 inch gantry material looks really odd.

Obviously with the different design I need to consider ballscrew placement and if I want to shield the rail, ballscrew. Since these haven't been pinned down I focused on a first pass design. On my own review it needed some additional span support.

Did the concrete and rebar reinforcement experiment last night, giving it some time to cure to measure improvement using the pretzel pipe.

Bought a chopsaw, Taskforce ain't bad for the money, smooth movement, good clamping, ok angle setting, I can make it bog. The cuts are far better and feel safer than using cutoff wheel on grinder.

Miss the pipe barge a little but not too much.

[dertsap]

wow ,you have some serious cutting and welding ahead of you

[jsage]

Yep,

Was thinking the same . I'm going to try some 1/10th scale for feasibility to optimize and minimize the complexity figure out how to incorporate missing structural detail. Jigging, and a tool I recollect for mating round tubing might make it tolerable. It seems it is always hard to get away from the chicken and egg problem.

[jsage]

Today I'll do a little experiment to what the deflection rate is for the 1" steel pipe I have available and see what magnitude of stiffening etc I get from the design, addition of internal concrete dampening. Should be interesting. Still looking for post on pdf mentioned. Will put under resources.

[jsage]

Resources used in this project

Rapid Machine Design: Key topics: Deterministic Design process, Finite Element Analysis (FEA), dampening http://www.mech.utah.edu/~bamberg/re...e%20Design.pdf (200 pages worth reading)

http://oneoceankayaks.com/madvac/madvac_index.htm High Precision 4X8 Metal capable
https://www.onsrud.com/home Specialty End Mills
Ballscrew Basics Ball Screws

http://www.rockfordballscrew.com/bss.htm Ball Screw Selection

[jsage]

Steel tubing:

Did some very basic analysis on the characteristics of the steel tubing. Outside diameter approx 1 3/8" wall thickness 1/8". Approx 1.5 pounds per foot.

Method: spanned a 6ft section over two uprights with two commercial buckets set 16 inches apart with a home made plumb. Measurements done with cheap mechanical ruler. Measured filling with water and removing water, consistent in both directions. Some increments interpolated since the process was a bit tedious.

Did a quick measure with 1/2 the span and the deflection decreased by more than 1/2 (approximately)

Next step add concrete then rebar. Then test actual design. Will probably do harmonic test and dynamic test if possible.

Conclusions were that an unmodified pipe with large span did experience significant flex under higher static loads. At approximate 100 pounds the 6 ft length flexed .186 inches. So I'm more comfortable that I am not overbuilding unecessarily.

Had a small epiphany today on how to measure deflection in an easier fashion. As Dr. Evil would say "Laser". I have a "mini laser" from an air rifle. set perpendicular to pipe and center. Parallel might be more interesting. Mark initial level then just add water and mark the movement. Might add a glued on flat marking piece to simplify measurements.

Never found that damn "laser" but I did find a local steel supplier who has what I'm looking for at the right price. The steel composition and characteristics need to be figured out but this what I found a the Metal Mart.

Damn have my quote for roofing but not the steel prices. It's primed and inside at least it looks cold rolled.

Anyhow 4" x 4" by 24' 11 gauge ran $76

The base works out to $234 with tax
rebar and concrete will be extra

$40 for rebar
$40 for concrete (horizontal structures)

So I expect when it's said and done approximately $500

[jsage]

Below is a first pass spreadsheet which should allow you to compare desired features versus expected version capabilities
2nd pass

[faststeve]

Use one large steel tube instead of that small tube welded truss. Don't you realise steel bends where you weld it !

That thing would be bent and twisted like a pretzel.

[mxtras]

I, personally, can not imagine welding that thing up and having it resemble anything other than a pretzel - especially with many of the tubes having welding performed only on one side down the length. The structure will resemble a bannana unless you have serious fabrication experience. Just my impression.

Scott