Small gantry planer style milling machine

[tredders]

I am considering making a small gantry planer style milling machine with a similar capacity to a BF20L mill drill.

Thought about getting the stock mill drill but was put off by what looks like a relatively weak connection between the column and the base. I'm in Australia & we don't have access to the sturdier looking Grizzley machine.

I'm planning to use square and rectangular tube steel and some flat bar to fabricate the frame - the uprights of the gantry and the beam below the table between the uprights made from square tube and the outriggers on the base from rectangular tube.

Instead of welding it together, I'm planning to bolt it together with heavy gauge angle iron/flat bar and lots of fine thread high tensile bolts, so as to avoid any heat induced stress. Will get parts surface ground before mounting linear rails.

My question is whether to use steel that is 100 x 100 mm by 10 mm thick, or 75 x 75 mm by 6 mm thick for the square tube and corresponding sized rectangular tube. Is 100 x 100 x 10 mm thick overkill?

What am I going to use it for? general home shop metal machining.... just a hobby.

Thanks for your thoughts on the subject.

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[tredders]

OK I'll take that as a no, 100x100x10 tube isn't overkill.

[hanermo]

100x100x10 is the minimum.

The problem is not strength it is rigidity.
100 mm square is very flexible in torsion ie twist and bend.

Plan for 50x strength vs load.
Almost all milling machines and lathes are like that.
There is an excellent reason.

[tredders]

Thanks hanermo.

[handlewanker]

A sketch.......my kingdom for a sketch, then we'll know what you're talking about.

Is it a gantry router or a mill???......both have attributes that are specific for milling steel.

A gantry router design is totally different to a mill for very definite reasons.

Oh, and what is your budget?

My opinion.....weld, don't bolt.
Ian.

[tredders]

Thanks handlewanker
I'd like to be able to put a sketch on the thread but after half an hour of playing with Sketchup2017 I get a sore head. Are there any CAD programs easier to use. S'pose it's like a lot of computer things, easy if you know how.
I'm planning to build a small mill, definitely not a router.
I'm curious to know why you say weld not bolt, as I've read that the welding induces stresses which can only be relieved by heat treatment. Sounds messy. I don't weld so that's a factor in my thinking.
I get a lot of satisfaction from metal machining as an absorbing hobby.

[handlewanker]

Hi....just as an example of what welding can do.........weld 2 pieces of steel together....can be angle iron, square steel tubing or just plain flat strip etc.......there is nothing that will surpass a welded component for simplicity of the final object.......with any other method such as bolting.........imagine the end result.

I have a few ideas on mills but as they're mostly in sketch form and hypothetical designs I won't bore you to tears.

On the subject of sketches........I use a Wacom Intuous3 graphics pad and a simple graphics program called Microsoft Paint that is present on practically all Windows computers.

You do need a graphics pad to sketch with as a mouse is just too coarse in the resolution and too jittery for fine detail.

The purpose of a sketch is purely to envisage the form that you have running around in your mind but do not want to sit for hours doing a formal sketch, unless you have very real CAD skills and know how to use it.

It used to be called back of envelope designing etc.......the freedom to doodle with a stylus like a pencil on infinite sheets of paper opens up your creative talent and once you have a gem of an idea formalised you can then get more formal with Fusion 360.....whatever......you can also get the same effect with a white board.

So all we want to see is the proposed layout that you think will shake the World.....LOL.........you want to build because you like to or for economy......no other reason.....it's all been done before in one form or another.
Ian.

[tredders]

Well at least I have a graphics pad now. Waiting for new charger for laptop as the charger and laptop had a spontaneous compatability issue.
A sketch is in the digital pipeline.

Hi....just as an example of what welding can do.........weld 2 pieces of steel together....can be angle iron, square steel tubing or just plain flat strip etc.......there is nothing that will surpass a welded component for simplicity of the final object.......with any other method such as bolting.........imagine the end result.

I have a few ideas on mills but as they're mostly in sketch form and hypothetical designs I won't bore you to tears.

On the subject of sketches........I use a Wacom Intuous3 graphics pad and a simple graphics program called Microsoft Paint that is present on practically all Windows computers.

You do need a graphics pad to sketch with as a mouse is just too coarse in the resolution and too jittery for fine detail.

The purpose of a sketch is purely to envisage the form that you have running around in your mind but do not want to sit for hours doing a formal sketch, unless you have very real CAD skills and know how to use it.

It used to be called back of envelope designing etc.......the freedom to doodle with a stylus like a pencil on infinite sheets of paper opens up your creative talent and once you have a gem of an idea formalised you can then get more formal with Fusion 360.....whatever......you can also get the same effect with a white board.

So all we want to see is the proposed layout that you think will shake the World.....LOL.........you want to build because you like to or for economy......no other reason.....it's all been done before in one form or another.
Ian.

[handlewanker]

Hi....if you have an Ipad you can down load the app Sketch Book Pro....costs about $10.....I use that mainly for sitting in the chair and doodling ideas while listening to the music files, you'll need a stylus.......the rubber tip type are OK but not too easy to make good sketches.

I haven't found a way to move them over them to my desktop as a J peg file.

I also bought a Samsung Galaxy Note GT N5100 tablet because that particular model has a cordless and battery less pencil type stylus built in and gives you a pencil sharp sketching ability using an onboard app called Notes.

The Samsung has a 200mm diagonal screen which is approx. 110mm X 170mm...big enough for doodling and the battery lasts for ages....it's also very portable and I use it mainly for creating G code programs in the garage as you can hand write and erase as you develop a program before compiling it with Notepad on the PC and saving it to a flash drive.

BTW....even the most mundane weld with steel will hold better than a bolt together item, and it's a skill that you can develop very quickly with very little outlay......the cost in materials for building a machine with welded joints is quite inexpensive and fast too......mainly in the square tube type.

However, if you have a preference to constructing with aluminium, then I would strongly advise against welding unless you have a high skill rating with ally welding.....it's not a very forgiving material or cheap compared to steel.,,,,,steel also has the weight factor to give you mass and make the frame rigid.
Ian.

[hanermo]

Nah... no need to weld.

Bolted is vastly more than necessary.
Even glued with industrial stuff would work.

A machine tool is a lightly loaded stressed-sking structure.
Max loads on machines are about 2% of yield strength.


Ian is right that the welded one is much stronger.
The point is that it does not need to be, since loads are minimal vs frame strength.
My z-axis frame is about 50 metric tons "strong".
50 tons on the z axis, would do it zero harm.

Probably, it could take 100 tons++ partly.
It is all bolted together.
Real loads are 100 kgf or less, 1000 kgf max.

I used welded structures in 2005-2008, and now use all bolted.
Unless 2 pieces slip in relation to each other, the union is solid.

Even tiny 6 mm bolts are much "stronger" than needed, and tiny 5 mm shcs bolts easily distory my 50-metric-tons strong frame.
I use == 10 of 5 mm shcs bolts to bend the frame straight.
These are drilled and tapped into the frame, permanent.

Then, machinist square on top, adjust screw until flat, leave, done.
Frame main members are solid 2400x300x20 mm tool steel flats, on edge.
2 of, with 35 mm linear rail on top, from hiwin.
Total height 200+35 = 235 mm.

I cannot build really flat in z, or have perfect floor or supports.
So I built-in jack screws to adjust it.
The square rests on the linear guide rail from hiwin, and is a precision ground surface.

A 5 mm shcs bolt == 200 kgf force.
2-Fingertip pressure bends a 1000 kgf bridgeport table, 4" thick cast iron, more than 0.03 mm.
Fingertips == 10 kgf.
Try it.

E.
Hitting a running 5000 kg modern cnc, say a HAAS VF4, when running, leaves a visible divot in the cut.
Reason:
The VMC bent.

This comment re:rigidity, to me, came from Gene Haas, who owns Haas automation.
And builds more machine tools than anyone else in the OECD world, by nr of machine.
About 1000 per month.

BTW....even the most mundane weld with steel will hold better than a bolt together item, and it's a skill that you can develop very quickly with very little outlay......the cost in materials for building a machine with welded joints is quite inexpensive and fast too......mainly in the square tube type.

[handlewanker]

Hi......as regards the strength point of view for weld or bolting......drilling and tapping and making pitched holes just to clamp 2 pieces of steel together is for the birds.....my opinion entirely.

Until anyone has drilled pitched holes both for tapping size and clearance that align with other pitched holes and tapped some of them too, and made sure the structure stays aligned by dowling it, it will soon become apparent that the ease that a welded structure can be put together is without compare.

The big bogey facing most people is the thought that after the structure is welded it MUST be heat treated to remove the locked in distortion that welds produce........locked in stresses stay locked in when the welds cool.....it's only when you significantly machine the structure that the welds cause a problem.

In all the years previously when I welded structures in industry, at no time was heat treatment considered necessary........I worked on many structures that GMH and Ford motor companies had that were welded and left as is and assembled into large linear transfer machine without a drama.

Welds do not move after they cool, but subsequent machining will make them do just that.

Expansion and contraction are the enemy, and anyone doing a continuous weld on a structure of many parts will soon be aware that expansion moves a part and welding locks it there......contraction will pull the structure out of shape immediately it cools......the answer is to allow the part to cool, or cool it before proceeding to do the next weld.

I weld progressively and cool a part in water to ensure the expansion has resided before proceeding to the next section..........cooling a steel welded part will not crack the weld.....blacksmiths do that all the time when they work steel at the forge.
Ian.

[tredders]

My rough concept sketch, minus spindle and table.

[handlewanker]

Hi, all well and good if you can make it like that......as you indicate that the main construction is on square steel tubing.....there is a lot more infrastructure to get to that point.

I don't think the design as shown is practical or achievable, as a welded structure or more difficultly as a bolted structure.

By the time the spindle stickout from the crossbeam is added to the sketch you will find the uprights will need to be moved back almost to the end of the base frame to allow the full travel of the table under the cutter.

It doesn't matter how big or small you make the machine, there is a rule of proportions that cannot be overlooked or sidestepped.

That is just my opinion......if everyone constructed to the same design you would only need to copy what's already been made, but as you want to walk a different path........that is your choice, we only look on to see what you are up to.

I have ideas of my own as to what makes an "ideal" machine, but I don't want to dictate as to what I think should be done.......mostly I'm a law to myself and have fixed ideas for steel tube working.

BTW......I've said this before, but am saying it again........when you design a machine like a moving table CNC router, you must start with the spindle as the centre point of the design and design around it to give the various travels and framework support.

This is because the power of the spindle is dependent on the size of the motor/spindle package and the area it occupies on the X axis crossbeam.

You'll be looking for the most powerful spindle drive in the smallest package.
Ian.

[tredders]

Thanks Ian
I agree that the vertical posts need to be further back towards the rear of the base.
With the spindle I've gotten as far as acquiring a 1.5 HP DC magnetic motor from a treadmill, and have yet to get the driver for it, but I've passed a treadmill retail store a couple of times and I'm planning to call in and see them about getting the control for the motor. It weighs about 7 kg with a flywheel.
I've seen a suitable looking spindle with an ER collet holder & no housing on line. I could make the housing, but I'm not confident it would be up the the recommended level of accuracy. Then there are the ready made spindles rated to umpteen thousand rpm. I don't expect I would be using my spindle at much over 2000 rpm. But it would be sure to be more accurate than something I'd make.
For a time I contemplated getting an Optimum BF20lv mill drill and the two things that put me off were that the vertical column doesn't appear to be rigidly mounted to the base and it would be top heavy.
Years ago I had a round column mill drill and don't want another one for obvious reasons. I also had a serious turret mill for a time, but it was too big for my purposes then, and much too big for me now.

What I want to make is something with a similar capacity to the bf20 mill drill, but a lower centre of gravity and hopefully more rigid.
I appreciate the comments about the pros and cons of welding and how to avoid introducing stresses.
I'm still a little bit inclined towards fine thread nuts and bolts because I like the idea of being able to tweak out error with some adjusting screws in tapped holes in a bar bolted beside the posts.. I figure the potential saving in the effort of scraping or shimming the substrata of the linear rails is enough to compensate for the effort of bolts.
My budget is around about what I would have to pay for a bf20 mill drill plus base.... say $AUD2K. If I can spend less I will put the saving towards computerizing it later.
The Hiwin 20mm linear rails look like they should work well enough.
I have no interest in doing it "my way". Anyone else's way is probably better, especially if they've got some experience.. All I want is a machine that works well and is compact and economical.
I have two other projects to complete before starting this... maybe 6 mths.
Thanks

[handlewanker]

Hi, I know where you are at........I started making a 3025 CNC router using steel tubing primarily with the idea of getting into CNC before I shuffled off etc.

Before that I invested a fairly large sum to buy a CNC mill with lots of options from a seller in China.....long story.....and after 2 years waiting decided to build one myself in case the original purchase fell through as has been noted here on the forum.

So the mill arrived and I put the build on the back burner, maybe to revive it one day as I like building things.

One thing I'd like to stress.....you have to decide right from the start what type of work and material you intend to apply the machine to.

If you intend to mill steel, then a router type is not on the cards......despite what some claim they can do......mills are for steel .....aluminium is at best for CNC routers and very rigidly made too.

I went against the grain and decided to make a small CNC router to mill steel, but in no way can you match the capability of a column mill to a gantry router.

You can get part of the way with a moving table router as the main structure is almost all in one piece and can be made very rigid compared to a moving gantry type.

BUT.....the starting point has to be the spindle and what it's going to do.......water cooled high speed spindles are not suitable for milling steel at low RPM due to torque that is practically non existent at low revs.........column mills overcome this by having a separate motor and belt driven spindle......their design layout caters for this.

So, any motor that is speed controlled by a VFD is totally out for milling.....you won't get torque at low revs etc.......if you intend to utilise the high speed characteristics of a BLDC motor and VFD you will be thinking in terms of carving and light aluminium work.

At some point you will need to do a fair bit of machining, so some machine or other will be needed and that means a lathe and a mill or someone who can do the machining for you.

I would say $2K for a machine would be far from the target.......think in terms of at least $5K eventually for all the materials.... and some tooling too, but that can be spread over the build time.
Ian.

[tredders]

Thanks Ian.
I get the impression that anything fabricated from heavy tube steel is going to work like a router and won't be able to remove steel much better than the vertical slide I use in my small lathe.
Sounds like you've saved me a lot of expense and time, and I'd be better off looking for something in the ready made mill drill range.
Thanks again.
David

[handlewanker]

Hi, I wouldn't dismiss the steel tube build purely because it's not conventional...........as I said, if you/as you are wanting to build with a moving table design this means you can make that one component that separates all routers from one another.....the uprights supports that don't move, so they can be practically solid material or more practically with thick wall steel tube and buttress bracings etc.

The milling cutter will try to make the upper parts of the router move and this is where vibration takes place.........eliminate that aspect and the build takes on another meaning.

You just can't add enough material to a column or router uprights and not create a rigid and stiff support.

It's brace it here and there and wherever the twist or deflection forces are likely to move it.

Even a buy in item has drawbacks.....a low initial cost can give you a lack of mass and rigidity of the machine.........the tendency for the manufacturer to reduce wall thickness in castings to save on costs only gets you a weak structure.

As a matter of interest, the machine I started building cost approx. $150 for the steel tubing and that was enough to build 2 machines.......it was cheaper to buy full lengths and cut it up myself at home than get ready cut to length shorter pieces.

I'll attach 2 pics of the build I was on in the loose assembly stage before welding and prior to putting it on the back burner......I first made a full scale model in Polystyrene foam sheet to see how the layout worked mainly for the travels and to see how the various tube sections would be fixed together.

I found that making a model precisely as it would be made from tubing gives you a full insight as to the practicality of the design.....and you can cut and re-glue if the proportions turn out wrong.......you can get a better feeling for the part when you see it in the flesh.
Ian.

[tredders]

Thanks. The photos are helpful. I think my project will go into the incubation phase for a while and I'll browse around this site to learn more.

[handlewanker]

Hi....don't lose heart....the designs for CNC routers are pretty much the same, just the material varies.

If you're thinking of milling anything hard I'd definitely stick to the moving table design......moving gantry types are more suited to wood etc.
Ian.