Was about to get a toy- then I did some research...

[NeoMorph]

Another thing to think about is I am 100% guaranteeing that any machine you design and build will end up getting modified in some way after you get your first cut chips.

I think I spent the first year either pulling my machine apart and making minor alterations like packing the interior of the extrusion and bolting the gantry beams together to increase rigidity and reduce harmonics, to bigger alterations like removing the old Z axis and replacing it with a stronger C beam and replacing the aluminium gantry uprights with strong steel ones. This reduced a LOT of design problems with my original build yet I’m still not 100% happy.

What I mean is, until you get some experience under your belt it’s hard to know what you want from what you NEED to make your machine do what you want. I’m still very much a novice yet have managed to improve my machine a lot over the last few years.

[Juranovich]

So a 1.25:1 ratio would be like a 12.8mm pitch which at 750rpm would give 9600mm/min which is a nice area with good amount of torque.
[...]
Spot on, on both accounts, except using the motor calculator. The key to speed is low inductance motors with plenty of volts wired in parallel.

Just to get my head around this- if 1m/min and 750rpm are good values for general wood working, what would be the sweet spot for detailed work (eg 3D engravings in wood) or the occasional aluminium job?

With regards the stepper size- what would be the optimal torque rating for the machine to be balanced (considering the consensus seems to go against 2.4nm)?

On a side note- thank you for the detailed discussion, since I’m new to this it sometimes feels I’m designing blindfolded as I don’t even know what parameters I should be aiming for!

[Juranovich]

What I mean is, until you get some experience under your belt it’s hard to know what you want from what you NEED to make your machine do what you want. I’m still very much a novice yet have managed to improve my machine a lot over the last few years.

I hear ya! But isn’t it lovely to overthink things especially when you don’t yet know anything? Even though I constantly pull myself out of that rabbit hole, I keep falling in...

.I AM THE FINAL WORD. . .

Also- I AM THE LAW!!!

[JAZZCNC]

Also- I AM THE LAW!!!

No No No I'm most definitely more THE OUT LAW.!!

Just to get my head around this- if 1m/min and 750rpm are good values for general wood working, what would be the sweet spot for detailed work (eg 3D engravings in wood) or the occasional aluminium job?

Well not sure where your getting 1m/min from but giving specifics for sweet spots for things like 3D work isn't really possible because it's material and cutter dependant, plus 3D work requires a slightly different machine setup to get the best from it.
3D work tends to be lots of really short fast moves with very light depths of cut, so you tune the machine differently and biased more towards acceleration than speed if doing lots of 3D work.
Velocity is not so important for 3D because the moves are very short so even if you had a High feed rate set you'll never actually reach that feed before your at the end of the move and onto the next. So to increase the feed rate it's actually better to lower velocity and increase acceleration. So now the machine can accelerate faster and reach a higher feed rate before the next move comes around.
Because of the nature of 3D jobs being made up of lots of short moves a properly setup machine can shave hours off a job. The simple rule is that you can't have both high acceleration and high velocity, setup is always a trade-off between the two.

Aluminum on the other hand just requires correct feeds and speeds based on the tool and material type and machine setup don't really play much part because the feed rates are so low compared to wood or soft materials there is plenty of torque available with a machine set up for a balance of speed and acceleration.

For instance, I have 2 different profiles one for general work with a balanced setup of speed and acceleration, the other set biased towards acceleration just for 3D work. When doing 3D work I just load the different profile and I'm set up for 3D work.

Now if you want me to make this simple for you then here's what I would use in the machines I build for general woodworking/aluminum use.

16mm Dia x 10mm Pitch screws for machines under 1000mm length with 1:1 ratio using belts to connect to motors. 20mmDia x 20mm Pitch with 1.5:1 Ratio for machine up to 1600mm.

NEMA 23 4Nm for 16mm and 20mm with twin/screws motors. For 20mm with single screw then 6Nm Nema34. Both with coils wired in parallel.
Look for motors in the 2- 4Mh inductance range when wired parallel.

50Vac or 80Vdc Digital Drives with 68Vdc PSU for Nema 23. NEMA 34 with 80Vac or 100Vdc drives. Both using Toroidal Transformer based PSU.

These are proven specs used on machines I build which are used for cutting materials ranging from cardboard to Aluminium and Brass on a daily basis working 12hr plus days 7 days a week in some cases.

[NeoMorph]

I hear ya! But isn’t it lovely to overthink things especially when you don’t yet know anything? Even though I constantly pull myself out of that rabbit hole, I keep falling in...



Also- I AM THE LAW!!!

My problem is when I overthink, it develops feature-creep in any of my designs and a simple rowboat turns into the Titanic (with associated problems included). 😳

If there is one piece of advice I could give it is if you are aiming to make mainly wood and soft material things GO BIG... as in get as big a footprint for your XY as possible. If you are aiming to make parts out of aluminium and steel... then GO SMALL as smaller equals more rigidity. As most hobby CNCers can’t afford a cast iron bed or have the skills of people like This Old Tony then a small mini-mill is actually better.

What threw me about bed size was how much you lose to the gantry and the dust boot. As I put mine into an enclosure I also wish me from the future had turned up and convinced myself to make the enclosure taller to give the dust extractor hose and router power room to move easier (I found keeping the mains lead away from the other wiring stopped any spurious signals getting onto the limit switch wiring... before I had the thing triggering random alerts all the time).

I also put onto isolation into the limit switch lines. I can’t remember the last time I had a spurious signal get through and trip the alarm.

[NeoMorph]

50Vac or 80Vdc Digital Drives with 68Vdc PSU for Nema 23. NEMA 34 with 80Vac or 100Vdc drives. Both using Toroidal Transformer based PSU.

These are proven specs used on machines I build which are used for cutting materials ranging from cardboard to Aluminium and Brass on a daily basis working 12hr plus days 7 days a week in some cases.

*DRRRRRRRROOOOOOOOOL*

I would love drives like these. Unfortunately not everyone can afford drives and controllers that can handle them.

I’m disabled person who had to take medical discharge in my late 20’s because of a deformed gene causing something that is now known as Hypermobility Spectrum Disorder.
So I basically live on a disability pension. Saving up for my Ox took me two years before I could order it... but I’m glad I did. Ooznest manuals are simply the best (especially when stoned on morphine 😂).

[Juranovich]

Well not sure where your getting 1m/min from but giving specifics for sweet spots for things like 3D work isn't really possible because it's material and cutter dependant, plus 3D work requires a slightly different machine setup to get the best from it.

My bad, meant to say 10m/min... effects of nightly writing...

I also put onto isolation into the limit switch lines. I can’t remember the last time I had a spurious signal get through and trip the alarm.

Of what I can see online non-isolated wiring seems to be quite an issue. Luckily, the electronics part is still some time away as that is the part I'm the least competent in (or more accurately "incompetent") and will probably be the most frustrating bit :)

Moving on to great news (for me at least) I’m finally able to post pictures of my design which is heavily based on ideas stolen from this forum! I planned on doing it in the build log section, but seeing the attention this thread has got I figure I might just keep it here (please correct me if I’m doing this wrong!).

So the basics:

- Total dimensions of the frame is 1000x800mm and gantry height 650mm as measured from the bottom of the frame to the top of gantry beam.
- The Z carriage is roughly 450mm high (extending some 150mm above the top of the gantry beam) and 200mm wide with 150mm travel (bearing blocks 300mm apart in the Z and 200mm in the X direction)
- frame consists of 60x120 alu extrusions on the sides and 3pcs 60x60 extrusions across (easy mounting of 20mm round linear rails ;) )
- gantry beam also 60x120 extrusions in L shape
- gantry plates and Z axis made out of 20mm alu, the thinner end plates/stepper mounts are 5mm alu
- the bearing blocks on the gantry plates are 250mm apart
- as discussed above 1610 or 1616 ballscrews drive X and Y, while 1605 will suffice on Z
- NEMA 23 (perhaps 4nm) on all axis as well as 20mm round linear rails
- Haven't decided on the spindle just yet, but should be able to carry something like a 2.2kW spindle (i.e. 5kg or so)

NB! All mentioned dimensions are not precise to the mm, but gives a good indication of the general size. Neither is everything perfectly aligned. I’ll anyway sort out the details as I make the final drawings in fusion. Also- I’ll model the final (balanced) version of the gantry plates as the gantry beam/Z axis design is finalised. Also2- stepper mounting plates will require adjustable fastening slots.





So to the specific questions I have in mind, I'll leave out the ones already previously discussed:

- Frame; I quite like the 60x60 extrusions across the frame as they give me clearance below the table (eg for X axis steppers), but would it be too flimsy? Looking at it now, I have quite some weight on the gantry vs the frame. Maybe worth beefing up the frame with 60x120 instead, or at least the two furthest to the front, leaving clearance at the back for steppers...?

- Gantry/end plates; online consensus seems to dictate 20mm gantry plates, but what about Z mount? Is 20mm overkill and would 15mm do in a machine this size? The end plates/stepper mounts are 5mm (as commercial stepper mounts seem to be in that range). As they're not subject to any excessive forces in my design I suppose 5mm is enough. Essentially they're only carrying steppers and the odd limit switch as well as providing additional stability in the corner joints of the frame.

- Other comments/critique?

[JAZZCNC]

*DRRRRRRRROOOOOOOOOL*

I would love drives like these. Unfortunately not everyone can afford drives and controllers that can handle them.

I hear what you are saying but £40-45 isn't a massive amount of money for a good drive. I've used lots of these low budget machines they are great value and work great. They cover a large range of motors including Nema32 upto 8Nm.

https://www.ebay.co.uk/itm/2DM860H-2...72.m2749.l2649

[JAZZCNC]

Going to show you some machines I've built that are all the same design but slightly different in size or Z-axis type/length etc dependant on usage but all share the same profile size. 45 x 90.
These machines were designed solely for woodworking and range in cutting area size from 600x400 to 1300 x 700 with a mixture of single or twin screws. However, all of them will happily cut aluminum as you'll see from a couple of pictures sent to me by customers.

Now I'm not showing you these and saying this is how you should build your machine but what I am showing is that this kind of profile size will easily do what you need so don't go stressing about if your 120 x 60 is strong enough or not. What's more important is how it's used ie: L shape gantry bolted together etc.
Some of these machines are used for business and running 12hr days 6 day weeks and have been doing so with minimal maintenance for several years.

Can I also strongly advise you to drop the round rail and go with profiled Linear rail. It's much much better and far less hassle. Don't spoil a potentially great machine for a few Euro more. You'll also get the extra back when you come to sell it as you'll be able to ask more for the machine and it will appeal more to those who know what to look for.

Also, move the ball-screw on the gantry to the top and motor below to keep the length of the drop plate to the shortest possible. Another thing you need to be aware of and one of the reasons why I use the Bosch Rexroth style profile with slot spacing at 45mm is that it suits BK/BF12 bearing bolt spacing. This means you won't have to make mounting plates or mess around drilling the profile.
It's these little details that can easily screw your ideas up or make things much harder than they need to be.!!

[Juranovich]

Going to show you some machines I've built that are all the same design but slightly different in size or Z-axis type/length etc dependant on usage but all share the same profile size. 45 x 90.

[...]

Can I also strongly advise you to drop the round rail and go with profiled Linear rail. It's much much better and far less hassle.

[...]

Also, move the ball-screw on the gantry to the top and motor below to keep the length of the drop plate to the shortest possible. Another thing you need to be aware of and one of the reasons why I use the Bosch Rexroth style profile with slot spacing at 45mm is that it suits BK/BF12 bearing bolt spacing. This means you won't have to make mounting plates or mess around drilling the profile.
It's these little details that can easily screw your ideas up or make things much harder than they need to be.!!

First off- those are some slick looking machines! Also, I never considered using a cross beam under the frame for dual stepper set-ups.

The round vs profile rail debate is one that has had me torn the most. Undoubtedly profile are superior in theory, in practice, however, I've been somewhat put off by the many worst case scenarios people have posted about when ordering the Chinese kind (which I strongly suspect is the only kind my budget allows). Second, being a first timer, I was hoping to get slightly more parallel mounting tolerance with the round rails (bc self alignment), and they provide more room for mounting ball screws on the same face (although that could also be achieved by spacers on the profile carriages). I'm curious though, in what way do you find profile to be less of a hassle?

Considering cost, downsizing to 45x45/90 extrusions might free up some funds that could be used on profiles... I might just have to bring out the famous abacus!

With regards the bk/bf12, I thought bolt spacing was something like 46mm in which case standard t-slot nuts wouldn't work? Or is it merely a case of using good ol' force?

I long favoured flipping the ball screw and stepper positions, but figured ball screw placement as centrally as possible relative to the gantry rails took precedence over drop plate length.