[GeckoSub]

Hi Craig,
As always thanks for your input and don't take this the wrong way. But I think you are looking at my build very much through your own shopping and importing experiences. From your posts, I know the prices you have been paying, your shipping fees and custom fees and seen through those eyes, I am with you.

But I can ship 1m3 from China to my door for about USD 215 and they don't care about the weight. I can pack a lot into 1m3 and I can consolidate a lot of the other stuff with this shipment. Customs... it's likely I wont get hit with anything.

Also, this base will be fairly affordable. (Will share price down the road if it all works out and holds tolerances). That said, just cuz the base wont ruin me, doesn't mean I can afford to order the wrong stuff for it and your point about the length of the ballscrews vs the machine size is certainly one that I pondered, too.

But as mentioned I can have them remachined - basically cut down to size. One of the vendors offered it for a fee and it sounded like it's something they often do. I have also been told by a machine builder in China that it's a fairly easy thing to do for someone in the know and if that's true - it really opens up my options. So, that's the approach now: Buy the best quality within my budget - which will likely be oversized and then have them cut to my spec. It's basically "only" the floating end that needs to be done, I would keep the driven end as is.

Now, the question is, is it not kosher having ballscrews chopped down like this? I mean, it may need a grinding operation in a lathe after a turning one but that's not really rocket science, either. And as far as I understand, the floating end has axial compliance anyways, right? So, what's important is that they get the new end 100% concentric to the rest of the screw.
Are there a bunch of horror stories about doing this?

[peteeng]

Hi Geck - Its fine to modify ballscrews with a machinist that knows how to do it. But why? If you plan the machine and get the parts, confirm the part dims then order the granite what's the difference? Heaps, you haven't had to mod anything and the machine ends up exactly off the dwg board. I used different (aluminium) motor mounts on my last machine. The supplier said they were identical to my usual steel ones. But the dwg supplied had a conflict on it so I waited until the mounts arrived. They were 5mm longer than "usual" If I'd committed to them I'd have to shorten my ballscrews, But since I now had them in hand I could make the wall 5mm longer and everything was kosher.. Peter

By the way when your figuring out working lengths of ballscrews you loss about 12mm due to the heads of the nut mounts or the motor mounts if you don't include them in the model. So if your trying to get accurate working lengths include the screws so you can pick up the clashes...

[GeckoSub]

Hi Geck - Its fine to modify ballscrews with a machinist that knows how to do it. But why? If you plan the machine and get the parts, confirm the part dims then order the granite what's the difference? Heaps, you haven't had to mod anything and the machine ends up exactly off the dwg board. I used different (aluminium) motor mounts on my last machine. The supplier said they were identical to my usual steel ones. But the dwg supplied had a conflict on it so I waited until the mounts arrived. They were 5mm longer than "usual" If I'd committed to them I'd have to shorten my ballscrews, But since I now had them in hand I could make the wall 5mm longer and everything was kosher.. Peter

By the way when your figuring out working lengths of ballscrews you loss about 12mm due to the heads of the nut mounts or the motor mounts if you don't include them in the model. So if your trying to get accurate working lengths include the screws so you can pick up the clashes...

First off, great to hear confirmation that a skilled machinist can cut them down, if need be

Why modify the ballscrews and not just adjust the machine?
It's just that I don't see that much in the lengths I need. A lot of the better stuff tends be longer than I want to make the machine
I think I only ever saw one set of nice C3s that would work for the Y with minimal change to the machine dims and they were gone, NOS at killer price so no wonder. In 1605/10, there'd possibly be a bit more to choose from but perhaps my machine just have a size where 2005/10 are mostly in other lengths.

And yes to remembering the needed extra length for mounts, coupling and even the nut! I have been using the Hiwin configurator a lot but there are actually a few different standards on the driven end. I think THK and Hiwin tend to have the same but still, not all of them have the most common one.
A set of C3 Hiwins offered to me that was a bit shorter in the driven end than normal, I think. So, if I used a standard MBA bracket, I would have a 16mm gap between the end of the spindle and end of the ballscrew when using the shorter spacer. Supposedly certain(?) longer couplings can span that without issue but it was an eye opener.

But it's also why I have the Y ballscrews, mounts and motor brackets sitting on an alu side plate. So, I still have room to move a bracket easily if need be and not be locked into having them mount directly to the granite.

[joeavaerage]

Hi,
If I bought the screws new (including the FK25 support bearings) $3000USD each, or $9000USD for the set of three. I got them for $1000USD for the lot, including shipping and I paid no customs.
It does not matter a damn to me about shipping or even cutting them down if I had to, but $1000USD verses $9000USD make a huge difference to the feasibility of the build. Quite frankly to have a chance to build
your machine to your desired accuracy then you will need to do the same, I promise you that is not easy no matter where you live.

I've built two machines, the first, a mini-mill about 11-12 years ago and my current machine I started three years ago. In both cases I have use C5 ballscrews, and I date the start of the build from the time
I had them in hand. In the preceding months I had decided what I wanted but until I actually had the ballscrews I could not finalize anything. Get the ballscrews, I don't care whether they are longer than needed
or whatever, you build your machine to suit what you've got.

Craig

[GeckoSub]

Hi,
I don't care whether they are longer than needed
or whatever, you build your machine to suit what you've got.

Craig

As always, thanks for your thoughts. The thing is, I care. I am not going to make a machine 200-300mm longer to fit a pair of ballscrews when there's a solid alternative.

Obviously, if ballscrews of a length that's within the scope of my machine size +/- a bit turns up, I will go for them, no doubt at all. but as said, for some reason, pickings are slim in the ~550-700mm "category". So, I may very well have them modified by the vendor's machinist (at less than $25/ea).

And now that it's confirmed that modifying the screws is no biggie, has zero adverse effects if done properly, I fail to see how that's a bad approach. For less than 25 bucks, I get a much, much bigger selection.

If people don't do this more often I think it might be a case of them thinking ballscrews are sacred or that they can't find someone to do it at a price point that's worth it. But again, that's not the case here.

[joeavaerage]

Hi,
well, you clearly know more about it than I do. Good luck to you.

Craig

[GeckoSub]

Hi,
well, you clearly know more about it than I do. Good luck to you.

Craig

Craig, I never said that. At least, not intentionally. If it can be read like that, I didn't put it well enough - sorry about that.

It's actually quite simple. The good screws are mostly 200-300mm longer than what I need and I, personally, would rather not stretch the machine that much. But by allowing myself to go with modded ballscrews I get a better selection and I end up with what amounts to a custom screw for not much more money.
I also clearly stated that if I do find good screws where I don't need to stretch the design much, of course, that's what I will be choosing.

Don't get me wrong, I think your advice is sound - especially so for the builders who are less set on keeping their machine at a certain (smallish) size. Having the ballscrews modified is indeed one more step and of course there's a risk they will bugger up the job. But it seems they know their stuff, so I am ok with being the guinea pig on this one.

Perhaps my last statement could be read wrong ("If people don't do this more often I think it might be a case of them thinking ballscrews are sacred or that they can't find someone to do it at a price point that's worth it. But again, that's not the case here.").

I didn't mean to be cocky with the "that's not the case here". I was merely trying to say that if my vendor can modify ballscrews cheaply and properly then the case is I have found someone to make it easy for me - and maybe others haven't been so lucky due to their location, lack of (affordable) job shops, etc and thus modifying a machine's dimensions rather than the screw is very likely the safer, easier, cheaper, smarter approach for many/most builders.

But for me, for this particular build, with the vendors I have found it might just be that I get to have my cake and eat it, too. Or I may be screwed, so to speak... We will see.

Now, for a bit of a detour:
Actually, a spearfishing friend of mine passed away about a year ago. I hope the following doesn't sound like I am sad about it for the wrong reasons. But he was an engineer at an energy company in China and used to take joy in being able pull all sorts of favors for me: Need some parts anodized, sure, send them my way and I'll add it to our next batch. Need the Chinese word for some machine type stuff or material so I can search for it online, sure - here you are. Need a handful of stainless parts CNC turned for your home made carbon fiber polespear, sure send me the file, etc, etc.
I can't even begin to describe how stoked he would have been to be apart of this endeavor. And of course, how cool it would be to tap into his network.

Actually, the assignment I mentioned a few posts back, the one which will pay for this machine will end in Indonesia. I will stay on afterwards and go spearfishing and I'll bring the polespear he helped make a reality years ago. With a bit of luck and some grit perhaps a Spanish Mackerel will swim close enough that I can pay a fitting tribute to him.

[peteeng]

Hi Geck - Here's something to aim at feed 60m/min in steel. Peter

https://youtu.be/cADWFl-_rwk

[GeckoSub]

Hi Geck - Here's something to aim at feed 60m/min in steel. Peter

https://youtu.be/cADWFl-_rwk

Oh, Titan... Don't know if I have it in me to click the play button, haha.
He definitely takes some getting used to for a grey Scandinavian like me.
I know he has his fans and a big following but how much is driven by real machining skills or how much is his bravado persona I do not have the skills to judge at all. Would be cool if he is the real deal.

That said, I like that outreach program he has (machining for immates type stuff) and that his stated goal is to get youths into machining. I think that's something to be admired. Reaching out, giving back, second chances and all that.

And I have seen some neat videos made by his less intense machinists, hehe, on smaller machines and some interesting things on work holding.

[pippin88]

Z Axis
You can't just design this later

Moving cars vs moving rails impacts the rest of the machine

With moving rails, you cannot get the Z axis above the bottom car (which is usually near the bottom of the gantry)
You have to know what height work piece and what TOOL LENGTH you might work with
People often forget the tool
This determines how high the gantry needs to be
Gantry height = workpiece height + tool length + distance from spindle nose to bottom Z car

Moving cars - you can get the spindle up above the gantry.
Gantry clearance sets you max work piece height

[GeckoSub]

Z Axis
You can't just design this later

Moving cars vs moving rails impacts the rest of the machine

With moving rails, you cannot get the Z axis above the bottom car (which is usually near the bottom of the gantry)
You have to know what height work piece and what TOOL LENGTH you might work with
People often forget the tool
This determines how high the gantry needs to be
Gantry height = workpiece height + tool length + distance from spindle nose to bottom Z car

Moving cars - you can get the spindle up above the gantry.
Gantry clearance sets you max work piece height

Yes, working on it these days. Also, you are right, I did forget the tool for a little while but once I had the rotary on the table and a rough Z-assembly with a moving gantry, it was obvious I was missing something. For that design, I did actually still have enough clearance in terms of being able to lift the tool above the part. The issue was the Z-outer plate collide easily with the rotary.

Still early days but let me share a few pics.
First of all, am I right in designing a moving rails assembly so that the bottom of the collet is flush with the bottom of the plate and rails?
Like this:


I am fairly sure the rotary will be around this height and quite a lot of work will be done on that rotary. Parts wont be huge, maybe 50mm in diameter. The tool stickout is 50mm here though:

But as you can tell, if I want the end mill closer to the chuck, that Z-plate will collide with the rotary housing. Unless, I place the rotary along the Y with the part and chuck facing away from me, which wouldn't be very user friendly. So, I guess that's one use case where the moving cars would be better(?).

And actually, as it is right now, that Z can't even reach the bottom (again, 50mm stick out on the end mill):


It can kinda reach a low profile vise. But of course at a loss of rigidity down there:


So maybe better to stick to a taller vise:


Honestly, the Z is not easy for me cuz I find I need to design them first and then move stuff around to visualize how it would all play out.

[GeckoSub]

Z Axis
You can't just design this later

Moving cars vs moving rails impacts the rest of the machine

With moving rails, you cannot get the Z axis above the bottom car (which is usually near the bottom of the gantry)
You have to know what height work piece and what TOOL LENGTH you might work with
People often forget the tool
This determines how high the gantry needs to be
Gantry height = workpiece height + tool length + distance from spindle nose to bottom Z car

Moving cars - you can get the spindle up above the gantry.
Gantry clearance sets you max work piece height

OK, so let me share the most extreme part I see myself trying to make in terms of height (let's not get into the challenges of chip evac, work holding and long skinny tools now, haha).

I am hoping I can cut some 18650 battery holders but it would an extreme case. The batteries are 65mm tall, let's add 15mm for a few mm of a solid bottom and some allowance at the top for a cap or connector of sorts. So, 80mm in total. So, 80mm stick out of the tool then double so the tool can actually pull out of the part, right? That's 160mm.
My clearance above the fixture plate in the current design is 235mm leaving 75mm. If I put the part in a low profile vise, I can retract the tool plenty:

Even the same with a tall vise like this:


Not sure what the takeaway is, though? Does this mean, I should go with the moving rails as it's supposedly stiffer and I can clear the tallest part I ever intend to make?

[jaguar36]

I would move your spindle mount to the bottom of the plate. Having the plate stick out below does nothing for you but get in the way.

Also looks like your design could use some more lateral stiffness, those flat plates on the ends are going to bend pretty easily.

[GeckoSub]

I would move your spindle mount to the bottom of the plate. Having the plate stick out below does nothing for you but get in the way.

I am admittedly just drawing this up from what I have seen elsewhere but I felt the same - and it would certainly help get around the rotary better. But I feel like I have seen other threads say it's best to do this way, but for the life of me, I can't find them now or remember the reasoning/.

Also looks like your design could use some more lateral stiffness, those flat plates on the ends are going to bend pretty easily.

Yes, they do start looking a bit skinny. They are 24mm now, likely 7075. I am lacking the words to describe this but I was hoping the forces would mostly just try to move them along the X so not so much bending nor twisting as the bolts should hold them in place.
I am not sure if it's common practice to just kinda match the stiffness of the parts - so, maybe would make sense for those plates should match the gantry and frame walls?

[jaguar36]

Yes, they do start looking a bit skinny. They are 24mm now, likely 7075. I am lacking the words to describe this but I was hoping the forces would mostly just try to move them along the X so not so much bending nor twisting as the bolts should hold them in place.
I am not sure if it's common practice to just kinda match the stiffness of the parts - so, maybe would make sense for those plates should match the gantry and frame walls?

7075 isn't any stiffer than 6061 or any other AL so it'd be a waste to use a more expensive alloy. You're going to have forces and moments going in all three directions as you machine so you need rigidity in each direction as well. More is better, doesn't need to match the other parts. The machine is only going to be as good as it is stiff in its weakest direction. Making one axis super stiff while leaving an other soft is not very useful, however you need to be looking at it as a whole, not just the part thickness.

[GeckoSub]

7075 isn't any stiffer than 6061 or any other AL so it'd be a waste to use a more expensive alloy. You're going to have forces and moments going in all three directions as you machine so you need rigidity in each direction as well. More is better, doesn't need to match the other parts. The machine is only going to be as good as it is stiff in its weakest direction. Making one axis super stiff while leaving an other soft is not very useful, however you need to be looking at it as a whole, not just the part thickness.

Yes, true, bigger picture than just that. But I was thinking those side plates shouldn't really see any/much twisting for example. The forces along the Y should be held in check by the ballscrews. My gut feeling was that the gantry could be pushed side to side along the X mostly and then tilted back and forth, but back and forth would also be in direction of those side plates where they are the stiffest and not across them where they are skinny.
I am really sorry, but I do lack the words to describe this and may very well also lack a deeper understanding of it all

I'd gladly take some experience advice/a shot on what to go for, though. Maybe this is a case for using steel which is indeed stiffer.

[GeckoSub]

7075 isn't any stiffer than 6061 or any other AL so it'd be a waste to use a more expensive alloy. You're going to have forces and moments going in all three directions as you machine so you need rigidity in each direction as well. More is better, doesn't need to match the other parts. The machine is only going to be as good as it is stiff in its weakest direction. Making one axis super stiff while leaving an other soft is not very useful, however you need to be looking at it as a whole, not just the part thickness.

Yep, I still mix up stiffness and strength sometimes. You're right. No advantage for 7075 over 6061 in this regard. I think steel could be an option, but I'd prefer something stainless as things will rust out here (Philippine island, close to the ocean). Either stainless plates or thicker alu.

[peteeng]

Hi Gecko - Stay away from 7075 it will corrode in front of your eyes. In machine parts terms no different to use 6061 or 5083 plate... I have used a lot of stainless for the same reason, stiff and won't rust. I hate rust & corrosion... Mild steel parts are fine just have to be painted properly.. size for size steel will be 3x stiffer so is attractive... Peter

[joeavaerage]

Hi,
my machine is mostly unpainted steel and cast iron, and it rusts a little. I live within km's of the sea and everything else rusts but my machine
gets a surface stain and that's about it.....and that's been two years. I think your worry about rust is misplaced, and certainly your budget is going to take a hit
if you start wasting money on stainless. Painted mild steel is fine.

Spend your money on what counts and don't waste it on things that don't.

Craig

[GeckoSub]

Hi,
my machine is mostly unpainted steel and cast iron, and it rusts a little. I live within km's of the sea and everything else rusts but my machine
gets a surface stain and that's about it.....and that's been two years. I think your worry about rust is misplaced, and certainly your budget is going to take a hit
if you start wasting money on stainless. Painted mild steel is fine.

Spend your money on what counts and don't waste it on things that don't.

Craig

That is soothing to hear. You're in Oz, right? So, also get some steaming hot days? It did really worry me. I have seen mild steel(?) painted gates, fence posts and roof structures disintegrate in less than three years on this island. Perhaps the quality of the steel can also be questioned as most people out here can only afford the very cheapest options.

I did make a tiny little "bench drill" out of alu extrusion and a no name 15mm guide rail to hold a small dremel-like tool. (Needed to drill some 0.2mm holes in plastic and doing it freehand snapped all the micro drill bits). But those guides rusted quite badly, too. But they are also the cheapest stuff from China. I do have a friend who imported a lot of old wood working machines from the US and they do indeed seem to only have that surface stain, no pitting.

The worry I had about painting mild steel is that I was assuming I can't paint the mating areas, so perhaps rust would creep in there after a while.