Yet another fixed gantry machine...

[Hartzell]

Hi!

I have given up my moving gantry plans and started all over.
I want a small, rigid machine for making panels in plastic and aluminium. Aircraft type of panels. And some wood decoration.
Work area around 16" x 9".
Accuracy is prioritized over speed.

First question:
What do you think about this construction?
http://www.romanblack.com/CNC/01_72.jpg

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[awerby]

That C.R.Onsrud machine looks quite sturdy. Are you going to build one of those? I imagine it would be able to cut small aluminum panels like you describe fairly well.

[louieatienza]

That machine is HUGE, if you don't know.... I believe 5' x 10' capacity, dual table, up to 40hp spindle.... I think for smaller machines fixed ganyry makes sense. The footprint can actually be smaller than the cutting area by mounting the linears and screw on the table itself, similar to a c shaped mill. You'll need clearance front and back when in operation however.

Check out CR Onsrud on YouTube, the Extreme Duty series is a BEAST,

[wizard]

Hi!

I have given up my moving gantry plans and started all over.
I want a small, rigid machine for making panels in plastic and aluminium. Aircraft type of panels. And some wood decoration.
Work area around 16" x 9".
Accuracy is prioritized over speed.

First question:
What do you think about this construction?
http://www.romanblack.com/CNC/01_72.jpg

The general concept is very nice. You should be able to scale the concept down for your machine. don't underestimate the need to have access to a machine shop or the reality that you will be paying big bucks to machine some of the parts.

[handlewanker]

Hi....big question is will you be welding, as in all steel build, or bolting as in aluminium extrusion build.

If you are designing from scratch using the Onsrud design as a basis, the material will dominate how you aquire parts and how you build it.

Bolting ally extrusions has it's own problem in that the sections are hollow and don't take kindly to being bolted from outside across the extrusion section without adding either spacers etc.

Working with steel on a fixed gantry/moving table design means you can make it as heavy as you want without having acceleration problems from excessive weight in a gantry.

For the part sizes you stated, a machine covering 300 X 450 with a Z clearance of about 100mm would be quite easy to achieve in 100mm square steel tubing and a 6mm wall thickness.

I'm involved in a 3025 build....slightly on the back burner at the moment.........and the build weight of just the steel tube frame in 75 X 50 X 5mm steel tube is almost 55 KG.......welding to come next.

The photo attached is the present loose assembly of the various parts before welding starts to see if the build plan is according to the design.

Total cost for the steel tubing used for 2 machines, as it's cheaper to buy in complete tube lengths and cut at home with a band saw or power hack saw, and the amount gave enough for 2 machines, was approx. $150 + some more 50 X 10 flat steel bar for the linear rail base mounts at $75....haven't got the exact figure handy at the moment.
Ian.

[Hartzell]

Thanks for replys!

I have made a simple sketch that shows what’s in my mind.
All welded 120x60x3mm steel tubing. Machined base for linears.
Y-linears mounted on top and bottom of the beam. I have read that a long distance between them is good, and so is having the spindle close to CG.

Just a beginning, but i appreciate your thougts about the concept.

Lot to do at work right now, writes more later.

https://drive.google.com/file/d/0B0EVIfv7x_SGdnhuUVU5Q3NGTnM/view?usp=sharing

[wizard]

Thanks for replys!

I have made a simple sketch that shows what’s in my mind.
All welded 120x60x3mm steel tubing. Machined base for linears.
Y-linears mounted on top and bottom of the beam. I have read that a long distance between them is good, and so is having the spindle close to CG.

Just a beginning, but i appreciate your thougts about the concept.

Lot to do at work right now, writes more

Nice! One observation, if you put your linear rails on the top and bottom of your gantry beam you will need a way to machine those mounting pads parallel. You really want to do that after you have all welding done on the beam. I would think long and hard about your approach here.

[handlewanker]

Hi, so very true.......always design from the standpoint of how your going to make it.

The principle of any design must be established first, then the design will work, otherwise it's a castle in the air.
Ian.

[Hartzell]

Good points.

What do you think of attaching the gantry beam with screws instead of welding? Maybe weld some thick plates to the beam ends for threads and do the machining on the linear mounts before bolting in place?

[hanermo]

I built beams, in steel, with a single tool steel flat heavily welded onto a tube.
Worked very well ...but..
I used very thick steel, that did / does not distort because the section sizes were chosen so that the errors dont creep up on you.

I mounted the linear guides on the side of the flat, with the sides in the upright = vertical direction.
Flat sides were 30x80 mm section side, solid tool steel.
Rectangles were 100x100 tube, 5 mm wall.
7018 weld.

Length about 1600 mm.
Should have made them thicker, in the next version I will add thicker flats, for bigger linear guides.
Going onto 35 mm (x axis is done in 35 mm, z axis bridge is being done (4 rail, bridge/portal mill) vs 20 mm guide rails.

My machine is for milling steel, and actual workshop use.

[handlewanker]

Hi, without being dictatorial and stating that it must be done this way or that, I'd suggest that if you want to bolt anything to anything you must first understand the potential to move as it's not a solid item in the end but a friction face on another friction face held there by the pressure of the bolts etc.

True, dowels can be used to locate the items from moving laterally, but the bolt area only gives you a point contact or spot face and as it is only a small percentage of the bolt face it's prone to flexing.

A fully welded structure can be as solid as a rock, even with thin sections and box construction etc......BUT.......somewhere along the line you have to machine certain faces to have accurate and square planes that won't move or go out of alignment.

In the 3025 build I posted in post #5 you'll notice that there are horizontal machined planes for the linear rails and vertical faces too.

Try getting that lot onto a mill in one piece and then machining the various faces and I'd have to say it's going to be a mighty big mill with a multi axis machining head to mill all the planes, bearing and ball screw seats in one setting.

Just to illustrate my choice, I opted to have the machine in two pieces......... base in one piece with multi cross base braces welded to form the basic foundation structure, and the upper bridge structure as a second bolt on item.

This then makes it easy to machine all the horizontal planes on the base piece in one set-up milling operation for bridge attachment, linear rail seats and ball screw mounting pads and afterwards a clean milling op on the bottom to make the machine sit level.

The bridge can then be laid flat on the mill table and have the faces for linear rails etc milled true in one operation.

A secondary operation is required on the bridge assembly to mill the bottom of the bridge upright supports square to the linear rail faces, and this is where an angle plate is called into play.......you can of course mill the base faces of the bridge uprights while it's on the mill table with the head of the mill swung over like a BRIDGEPORT head or on the table with a horizontal mill spindle etc.

Trying to do all those operations in one fully welded assembly would take sophisticated machinery, but it can be done quite easy if you have the skill etc.

This is just my suggestion for a build sequence without tears.

As I recall the title of the thread is "Yet another fixed gantry machine"......so it should actually relate to your design and how you intend to make it etc.......your design is totally different to the approach I'm taking, and is almost identical to the aluminium KITMILL design CNC router as sold on EBAY, a couple of photos attached to show what I mean.
Ian.

[wizard]

Good points.

What do you think of attaching the gantry beam with screws instead of welding?

Well not machine screws! You would be best off with cap screws that are fairly hefty. Those screws would need to thread into equally thick or better material.

Maybe weld some thick plates to the beam ends for threads and do the machining on the linear mounts before bolting in place?

Your basic layout isn't that bad but I'd still put some time into considering how you would machine it. How you would do that depends upon what equipment you have access too. You might want to consider an arrangement that places the gantry beam on top of the uprights and bolted in place. This requires bolting machined surfaces to machined surfaces.

You will likely have trouble finding a mill that can easily get to all the surfaces in the base if it is welded together. It might be wise to consider vertical piece that can be removed. That means more surfaces to machine and bolt together.

Another option is to face mount your linear rails instead of going top and bottom. Here the gantry would be a pre welded assemble looking a bit like the glyph for "PI". This single assembly could then be bolted to the base frame. You do loose a little bit with respect to the spread on the Y axis rails and if this is a big problem for you, you cam make the gantry beam bigger.

In a nut shell there is no one right way to build such a machine! Your general layout isn't bad but you need to consider how you will machine the components. As noted this varies with what you have access to machinery wise. In some cases guys have dismissed machining and instead gone with grouting to cheapen the build process. No matter which way you go you design must be "doable" with the process you use.

As an aside when bolting together such structures, nice wide flanges help a great deal. You don't want the structure rocking on the mounting screws. My suggestion would be 1/2" cap screws at a minimum and larger wouldn't hurt. Upon assembly those bolts need to be torqued down good.

[handlewanker]

Hi, I think this design is coming apart at the seams and is now gravitating to "need some advice on a design for a bridge mill to machine steel" and not "do you think this or that would work" etc.

Designing on the fly always leads to redesign and yet more redesign, usually after the first metal is cut.

My advice.....for what it's worth.....is if you do not have design qualifications and are not aware of the pitfalls of bolted/welded fabricated design and subsequent machining problems arising, then get a design engineer to draw up the machine to your specifications and a draftsman to lay them out, then someone to make it......it costs less and saves a lot of headaches that way.
Ian.

[LeeWay]

Ian, that borders on blasphemy. There are thousands of proven design concepts here on the Zone. No need to hire professionals and let them have all the fun. Design something. Then show it here. We will let you know where the design needs work. Right, Ian?

[handlewanker]

Hi, not quite intended to read that way.......that's the easy peasy way to achieve, but if you want to entertain then by all means post a design as how it's going to be made, but at the same time title it accordingly, or give it the correct thread title of asking for a design appreciation or advice.

So far nobody has commented on the design in post #1 as being totally impractical for milling anything except wood, plastics and perhaps with a prayer some aluminium, but in my opinion it is a bit flimsy and could benefit from increased material dimensions

I'm quite appreciative of innovative designs and materials in various combinations, but I assumed the poster wanted to actually make a machine to use as opposed to debating the various ways it can be done.......he did post a drawing of the proposed build........that indicates the first step has been taken.

I was quite looking forward to some new ideas on this build as I'm also indulging in an own design and build program.......sorry if I misinterpreted the title of the thread.
Ian.

[handlewanker]

Hi, I assumed the layout had already been established as the material had already been decided on, which means some critical loading factors have been applied........I'd be horrified if it was just a casual rule of thumb exercise in DIY......you don't want to get to the end part and find it needs to be extended, shortened or mangle by cutting out bits etc.

The design can fluctuate wildly if welding or bolting is anticipated as is now apparent.

I would suggest that alternative design layouts to the post #1 concept be proposed so that a real end product can be achieved.

A case in point......why use 3mm wall tube for critical load bearing members when 6mm wall is available?.....weight is not a "must not have" factor for fixed gantry routers.
Ian.

[Hartzell]

Hi

I think my initial post and topic is missleading. Sorry for that.

To clarify, here is my goals in list-form:
- It is a hobby project
- For making small wood, plastic and aluminim parts.
- No steel milling intenden.
- Hobby machine on a hobby budget so i´m not willing to hire engineers etc. This forum substitutes the engineer so to say.
- Will try to design the build to use materials i allready have.


I will talk to my friend who is helping me with machinig and come back here with an updated sketch.

[bhurts]

Just to clarify for Ian. The machine in the first post is a beast that would mill aircraft aluminum panels all day long. It has a 30 or 40 taper spindle with high hp and the frame is made of at least 1/2" probably thicker structural steel. It has a moving table and probably weighs 10-20 thousand pounds.

Ben

[bhurts]

Just checked there site. It is a 18hp hsk 63f spindle which is impressive. The base one piece of structural steel. The uprights and bridge are cast iron and it has a 3800ipm machining speed and 4800ipm rapid.

Ben

[handlewanker]

Just to clarify for Ian. The machine in the first post is a beast that would mill aircraft aluminum panels all day long. It has a 30 or 40 taper spindle with high hp and the frame is made of at least 1/2" probably thicker structural steel. It has a moving table and probably weighs 10-20 thousand pounds.

Ben

Hi.......I think we can glean from the manufacturers blurb what the capability of the machine is without wanting to have that model, but as a design it could be scaled down for a starting point and used to make what you will.

Getting the layout of the slides for the smaller scale is the hard part..........most times you'll be working with off the shelf materials, so scaling them will be the more difficult part.
Ian.