To do or not to do, can it be done? MK4 drill steel.

[Oldtech]

After spending a few months reading and studying... I have finally advanced to the level of "I know what I don't know"... maybe.

I've watched all the videos of the MK4 and think the dual box design gantry may serve my purpose. Here's the pie in the sky.

A multipurpose machine, mill, drill and plasma. Forget the plasma part for this discussion. I would like to bore mild steel 10 - 15 mm plate. I figure I'd probably have to change out the z axis spindle depending on the operation, a lot of details would need to be looked at there but now my question?

Could a dual box design like routercnc MK4 generate the forces needed to drill a steel plate using an annular bit? Holes would be 10 to 20 mm. I've got a need to drill large plates 1200 x 1200 mm.

Further spec's on the machine would be, milling plastic, aluminum, and wood.

Any help on threads, builders etc... would be appreciated.

BTW kudos on the MK4 that is some impressive work.

[routercnc]

With the right spindle on my machine it probably would, but the reason I went with that overall layout was I wanted a large cutting area for sheets of wood, but still be able to mill with it.

If you don't need anything that large then a either a regular mill style (column at the rear XY table in front), or a fixed gantry with moving table would be better.

Either way you would need a spindle with high torque and low rpm, in the hundreds of rpm for the annular drilling.

[Oldtech]

Fixed Gantry won't give me the versatility. I'm thinking of a spindle motor/gearbox like from a mag drill. The delimma is z axis design. Yours is the closest to what I've imagined but can it be modularized. Something I could swap out for high speed operations. I've even considered electro magnets to lock it all down during drilling. It's probably not necessary with your design although I don't think I would use any aluminum.

Thank you for your thoughts. You've built a great resource here.

[routercnc]

Depending on the accuracy you need to hold over time if you swap out a spindle then it might not go back in fully trammed. Maybe you can provide some kind of alignment pins or something, but it needs some thought.

Therefore another option is to have 2 spindles - have the low speed spindle in the main housing. Then on the lowest part of the Z axis have a thick plate hanging out the front with the high speed spindle in. This is cantilevered out, which is not so good, but might be good enough for the high speed lighter work. Some Bridgeport owners do this to give both options. Like this but hanging out the front ahead of the gantry beam:
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If you want all steel construction have a look at the Mori Seki 5000 for ideas:
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https://www.youtube.com/watch?v=XCET5zkA4cU

[Oldtech]

Yes I've seen the Mori. A feat in machining. On a more realistic feat, at least for the retired hobbyist I got the idea from https://youtu.be/8OTwT0WFBmg Adam Savage Test series. A dual head plasma router. Kind of like you suggested but I don't think it could handle the forces. I'll work on some concept drawings and get some opinions. Thanks again.

What kind of accuracy are you seeing between table extremes?

[Voicecoil]

I'm thinking of something to fulfill not completely dissimilar requirements for my next "big" machine. My current solution is a moving gantry with 2 Z-axes - a high speed cutting spindle on the front of the gantry and a slow speed drilling/tapping spindle on the rear.

[Oldtech]

Voicecoil, sounds a lot of what I'm thinking. I've considered the front / back idea would be interested in hearing a consensus on this idea. Have you done any drawings?

I've got so little experience with these machines I don't know what to expect. That's why I'm here. To glean whatever I can.

[Voicecoil]

No drawings done yet I'm afraid, it's just an idea in my head at the mo., based on what I've learned from making my little machine. I can tell you that it will have a pretty massive "extrusion" for the gantry though (likely 200 x 130mm), and will use the same dual ballscrew Z-axis arrangement to minimise the offset between the gantry and the spindle - even more important in this arrangement if you want both spindles to be able to cover a decent working area whilst keeping length to a minimum.

[Oldtech]

I assume you are talking steel gantry. That's heavy. What size ball screws? What are you going to use for a spindle on the drilling axis?

I ran a little test today and it requires between 300 - 500 pounds to make a 25 mm hole with an annular bit. Most mag drills have a +/- 1200 watt motor. Sorry for the conversions, I just took my bathroom scale and centered it under a piece of mild steel on my drill press. I couldn't find any data discussing the physics of annular drilling.

[Voicecoil]

Well no, I was thinking of using aluminium, but it will still be quite heavy! Ballscrews will likely be 1610 or 2010, haven't really though about the drilling spindle as yet. Your test on the drilling force (which is pretty huge) probably means a front/rear approach isn't the best as a couple of quick sums indicate that the twisting moment on the gantry is likely to cause significant errors - a "dual rail" gantry as in routercnc's design will obviously not suffer from that, the main deflection would be an upward bowing which shouldn't impact hole position too much.

[Oldtech]

Thanks for the feedback voicecoil, lots of talent on this site. When you said you were drilling I assumed a steel gantry because of the twisting issue, but what do I know. Yes I believe MK4 would be able to do it but I'm starting to think about the speeds I would sacrifice for other operations. I'm thinking about building a gantry across my fabrication table and doing some z axis experiments. Do you know of any practical guides on the torque delivery for various components, steppers, ball screws etc...?

[Black Forest]

Do you foresee doing many of the steel plates on a regular basis or is this a one time thing? And how many holes in the steel plates are you talking about and how accurate do they need to be located? I have an idea but I need more info.

I built this drilling and tapping arm for my fabrication table. I have interchangeable heads that mount on the arm. Hydraulic for the heavy duty drilling and tapping and air for the lighter stuff. The arm is raised and lowered to bring me into the range of the hole needed. For your operation maybe you need the location closer than what just a punch prick like I use on mine.
https://www.youtube.com/watch?v=glFhIVgZGQg

[Oldtech]

My son builds custom wood furniture and bends some exotic hardwoods. He's figured out how to bend ipe, usually considered unbendable but requires some very stout jigs. Ipe is one of the densest woods in the world in fact it sinks in water. He had one customer bend it for his swimming pool border and make a very elaborate deck. He also wants to be able to mill this stuff. It's more like milling aluminum than wood. So we have several cnc opportunities for plasma, drilling, milling, and routing.

One of the first items is to make a few fab/jig tables similar to the one in your video, 12 - 25 mm thick. They will have custom hole patterns not the standard square pattern. I figured since I'm going to build a cnc table why not cover that problem too. Essentially replace the mag drill and take a 12 hour job to half that maybe less. Someone will still have to sit and chip watch. I included a sample of one table idea.26719

I like your idea for the fab table though we could have some use for it. If this cnc drill table idea doesn't work out I might use your idea and mount a mag drill to your manual gantry for fab tables. It would definitely make positioning easier. Thanks for the ideas.

[Voicecoil]

Thanks for the feedback voicecoil, lots of talent on this site. When you said you were drilling I assumed a steel gantry because of the twisting issue, but what do I know. Yes I believe MK4 would be able to do it but I'm starting to think about the speeds I would sacrifice for other operations. I'm thinking about building a gantry across my fabrication table and doing some z axis experiments. Do you know of any practical guides on the torque delivery for various components, steppers, ball screws etc...?
A large thick-walled aluminium box section can have considerable rigidity and weight-for weight won't be a long way off steel, however it won't have the torsional rigidity to cope with the sort of drilling you want to do, leastways not with a 1.3...1.4m long gantry. I'm only thinking of making something that will drill (sometimes) & tap (quite a lot) up to 8 or 10mm in aluminium or maybe 5...6mm in steel, larger holes would be milled out.
Stepper motors are nearly always listed by their size and torque (e.g. Nema34 8.5Nm), ball screws have their maximum static and dynamic axial load ratings listed in the data sheet by Coa and Ca, it's worth checking these as it would seem they can vary between manufacturers for a given size.

[Voicecoil]

Just had another think about this, and it occurred to me that I forgot to ask one important question - how accurate do you want these 25mm holes to be? I said that my big ali gantry wouldn't be stiff enough, but I was judging that by standards for precision machining of stuff. I did the same calculations (using routercnc's excellent spreadsheet that's lurking somewhere on this forum) with a piece of 200 x 100 x 5mm steel box section and get a tool deflection of roughly 12 microns, assuming the centre of the drill is 150mm from the beam - would that be good enough for your purposes? FYI that beam would weigh something like 28Kg.

[Oldtech]

Plenty accurate. It's frustrating being old school and from the U.S. I have to constantly convert measurements as I read. I'm always thinking tenths and thousandths. The accuracy isn't that important probably +- .25 mm between centers. Thanks, I'll look for that spreadsheet.

The dual rail design is certainly more robust overall but the Z Axis would increase build time and interchangeability. I read Neale's AVOR build last night. I'm starting to think maybe a steel box like AVOR may be sufficient. Being a novice I need to pick my battle so the whole thing doesn't end up in a corner somewhere. Maybe Gen 2 when I've got more experience. I will probably tig weld much of it to keep down distortions but I don't see that as a problem. I can do a lot more discovery with steel much more economically.

Appreciate your help.

[Neale]

Seeing that you've quoted my design, I might as well jump in here! I am extremely pleased with the way my AVOR machine has worked out - much better than planned. As a model engineer rather than a woodworker, I've been doing a lot of work in steel recently. For example, cutting the external profile of small steel components (maybe 10mm or so square) and then turning them through 90 deg and slotting. However, I only have the usual router-type spindle nominally rated down to 6K RPM, and it's possible to get it bogging down and slowing (to the point that I have worn out carbide cutters) even then. So, I run at, typically, 7K+ RPM, with carbide cutters in the range 2-4mm. I would cheerfully cut a 25mm hole through steel with this - in fact, I have done through something like 3mm hot-rolled steel - but I do it with an internal contour cut rather than drilling out all the waste. My machine does fine with this, and certainly to the kinds of accuracy you are talking about. When I first saw your requirement, my immediate thought was that I would do it my way, in effect trepanning/annular cutting but with a small milling cutter moving in a circular path. I didn't say anything because whether or not this would work for you depends on a bunch of other factors, like how many, how fast you need to cut them, how deep, etc. From a design point of view, loads on the machine are much reduced compared with drilling but it would be much slower than a machine capable of putting a 25mm drill through steel. In fact, I wouldn't try to do that even with my vertical mill - that's quite some cut.

There is something else to remember, and that is that a CNC machine, properly set up and with appropriate ways to clear chips, will run happily without someone standing there doing anything. So the fact that a job might take longer is offset by the fact that you can be getting on with something else at the same time.

I'm rambling a bit, I know, but although I haven't carried out any formal analysis on it, my gantry design is pretty stiff and capable of handling the kinds of loads my spindle/cutter combinations can throw at it. YMMV!

[Oldtech]

Neale I was hoping you might reply. It's good to hear about the steel cuts, that is good news for cutting ipe, an extremely dense hard wood. As far as cutting the holes I could have 300 or more in 12 - 20 mm steel. Most holes are 16 mm. I put an image of a typical table jig in a previous post. The reason they need watched is because it doesn't leave chips it makes birds nests, and a lot of them. This is a stock video of an annular cutter and mag drill https://www.youtube.com/watch?v=N7Pef3zFj7Q in action. It only takes about 30 seconds to drill but a long time to clear and re position. If you look at the machine in the video I'm thinking of taking that motor and mounting it on the z axis for the drilling spindle, and a second z axis for routing.

What do you think of using rectangular tubes for x axis maybe 50 x 100 mm? Mainly for torsional load. I see you made your z axis out of aluminum. I'm thinking making that out of steel also, welded 5 mm plate. Assuming I can keep it flat enough. This is looking more like prototyping and cheap and easy seems the way to go.

[Oldtech]

Also Neale, your machine looks very stout, has the gantry weight presented any issues? I think you said you used NEMA 23 would 34 be better? Twin screws on Z axis?

[Neale]

I call my long axis X, and gantry is Y axis. Need to be clear about that to avoid confusion! X tubes are 100x50, supported at a number of points along their length to the main machine frame. No particular worry about strength there. Gantry is 3 off 50x50. Could have been 100x50 plus 50x50, but that's what I had left over! In fact, the twin 50x50 welded together is stiffer in the vertical plane than a single 100x50, I would think.

Again, based purely on my experience, 3mm is adequate for strength. However, as JazzCNC has pointed out elsewhere, it's not just strength that matters, it's also things like vibration and resonance. My machine does suffer from that at times and although it's not a major issue for me, I would probably go up to at least 4mm wall thickness just to reduce this effect.

My Z axis is, indeed, aluminium plate. I used 20mm Ecocast or equivalent ground finish tooling plate just because it is flat. I used 20mm as that allowed me to cut recesses into the plate for the Z axis ballscrew for clearance without unduly weakening it but it seems pretty stiff to me.With the Hiwin rails and bearing blocks properly arranged, I'm not sure that there is very much bending load and it is stiffened in any case by the spindle clamp block and partly by the rails themselves.

I am happy with NEMA 23. It's very easy to over-specify in this area and it's likely that NEMA34 would give poorer performance, bearing in mind that I want this machine for cutting wood as well, and also want decent acceleration for fine detail cutting. I have compromised by using 5mm lead ballscrews; 10mm would give more speed but lose torque. As it is, the motors hit max speed at about the same speed as the max ballscrew speed (to avoid whipping) so they are fairly well-matched; there's plenty of grunt and in practice, all that suffers is max rapid speed. NEMA 34 may have more max torque but have much more rotational inertia and internal inductance, which both reduce acceleration. OK for a mill, not so good for a router. If you do the sums, it works out that the torque needed to spin up the X ballscrews (all 1750mm of them, 20mm diameter) is roughly the same as the torque needed to accelerate the gantry, despite its weight. It's easy to forget that rotational inertia of the screws is a significant factor in all this; don't sweat over saving a few grams of gantry weight.

Why put twin screws on Z? For a "router", downforce isn't that big an issue although I can see that if you are looking at heavy drilling or similar plunge cuts, this might be a different matter.

All machines are a compromise and that's why a lot of us build our own - we can build to make those compromises in areas that don't matter too much to us and focus on what we do want. I wanted a machine capable of good 3D detail performance for engraving. Below is a first pass (don't have picture of final version) of a brass master I engraved for my local model engineering club. The recess is approximately 20x10mm, so the level of detail isn't bad for a machine designed to handle 4'x2' sheets of plywood. To do that using 3D V engraving needs good acceleration in all three axes; max cutting speed is only of academic interest! But I can also move at 5000mm/min when needed. On the other hand, you are looking to mass-produce large holes in steel but accuracy is not as high on your list, so while you are welcome to steal any ideas from my machine (as I did from others!) I'm not sure that you want to copy it.

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[Oldtech]

Thanks again Neale. A lot to consume. I looked at the difference between rectangular and square tubing and agree the benefit is negligible. I watched "This old Tony" video https://www.youtube.com/watch?v=jOvGv9aRKFs where he cuts steel with his build using closed C Channel on the gantry. He sand filled the frame and it is a fixed gantry. I'm sure a huge advantage and not comparing apples to apples for what I need to do.

[AndyUK]

Before using This old Tony as a source, watch this. About two minutes 30 in...


https://www.youtube.com/watch?v=Ogwp7zD59og

[Oldtech]

I'm not surprised TOT is going this route. I think he likes old machines and rebuilding them. If I had an opportunity and a bit of an inkling I'd do the same but it wouldn't meet my immediate requirements. I think what he is saying is a router isn't a milling machine nor is it a drill but my choices are limited short of resources $$$$. I also like the guy who built the granite router. https://www.youtube.com/watch?v=d3f3vknWj-w Now that is stable and possibilities are interesting. Again not now. That probably shouldn't be called a router.

That brings me to the granite guy claims on the Jianken spindle. He gives it much credit. Has anyone here used it. This video shows him doing, by mistake, a 10 mm deep 8 mm wide aluminum cut. https://www.youtube.com/watch?v=h9q6j7POgOI&t=982s

Pretty impressive for what might be called a router.

[Chaz]

I'm not surprised TOT is going this route. I think he likes old machines and rebuilding them. If I had an opportunity and a bit of an inkling I'd do the same but it wouldn't meet my immediate requirements. I think what he is saying is a router isn't a milling machine nor is it a drill but my choices are limited short of resources $$$$. I also like the guy who built the granite router. https://www.youtube.com/watch?v=d3f3vknWj-w Now that is stable and possibilities are interesting. Again not now. That probably shouldn't be called a router.

That brings me to the granite guy claims on the Jianken spindle. He gives it much credit. Has anyone here used it. This video shows him doing, by mistake, a 10 mm deep 8 mm wide aluminum cut. https://www.youtube.com/watch?v=h9q6j7POgOI&t=982s

Pretty impressive for what might be called a router.

Funy, I watched that same video last night.