Input for new build

[Lynge]

Hi.
After some trouble with a kit I ordered, I have decided to just design and build the damn thing my self

So, I was hoping for some input before I send out an order for the parts I need.

First, some pictures

The base, despite the purple color, its made from OSB or plywood.


The Y-axis.
This is sbr20, would that be strong enough? I could get it in sbr25, but I have trouble fitting that under the Y


base and X combined


Y-axis beam and rails


Y-axis backside with ballscrew and motor


Y and X meetup


Z-axis without frontplate


frontplate for Z with "spindle" The spindle is a 2.2kw watercooled chinese VFD type.


Complete Z assembly


Z assembly when extended. Just to show how the rails move and not the blocks. This should provide a more rigid outrigger right?


All the parts put together


Z and Y meetup

Also, here is the skp for it. http://dl.dropbox.com/u/23003345/z-axis.skp

With that out the way, I guess I should explain what I hope to achieve.
Apart from wood, I would very much like to milll aluminium sheets and blocks with this. Not at breakneck speeds of course, but being able to get a decent finish would be great.

The Y-axis beam is a steel girder. It was free at a scrap heap so it might not be the ideal material, but unbeatable at the price

Also, the Y rails are sbr16, will these be strong enough or should I upgrade to sbr20?
The Z rails are also sbr16, this should be plenty strong no?
I have 450oz motors. Don't know if these will have enough power to mill aluminium or even move Y-axis as it might be a little heavy.

All motion is by 1605 ballscrews.
How about whipping with ballscrews at 1500mm in length?

So any inputs at all would be very nice. Any upgrades or changes that would make a noticeable difference or maybe I am aiming too high?

[PaulRowntree]

I would start with thinking about the frame support. It looks like you are counting on the OSB sheets to make sure that your table is level, but I think that will not be nearly enough. If you put this on a table top with a warp, twist or bend, the X drives will skew accordingly.

Check out Nook Industries site; their screw catalog has speed tables to estimate max linear speed without whipping; it depends on how you want to secure the ends of the screws.

It is hard to make more detailed comments on a design without more dimensions.
Cheers!

[ger21]

I'd probably go with 2010 ballscrews

[Lynge]

ger21: How about RM2505? I can get those at almost no extra cost and they can use SC25UU blocks for ballnut housings.
But will 2505 be too heavy? I mean is it any harder on the motor to use a larger diameter?

PaulRowntree:
I see what you mean. How about a base set in concrete? And then maybe the OSB on top of the concrete to have something to screw into. How do you think that would work?

I will try getting some dimensions on the model. Any particular you had in mind?

[ger21]

The problem is that with 5mm pitch, it'll need to spin twice as fast as 10mm pitch for a given speed, The high rpm is what causes the whipping. While 2505 is better than 1605, if it were me, I'd want 10mm pitch, regardless of diameter.

5mm pitch will probably limit you to a max speed of 200ipm, maybe less due to the longer lengths. 10mm pitch should get you closer to 400ipm.

But will 2505 be too heavy? I mean is it any harder on the motor to use a larger diameter?

There's a lot more inertia with a larger diameter screw, which will result in slower accelerations.

[Lynge]

The 10mm pitch seems a little harder to find, but it should be doable.
The downside of it must be that the motors will need more power to perform the same task, just like a higher gear in a gearbox right?

Apart from the time it takes the machine to finish, is there any downsides to the lower speeds of the 5mm pitch?

Will I need the higher ipm for better part-finish?

[ger21]

The downside of it must be that the motors will need more power to perform the same task, just like a higher gear in a gearbox right?

Correct.
But I can't tell you whether you'll need bigger motors or not.

Unless you know how much weight you'll be moving, and how fast you want to accelerate it, and to what velocity, you won't know what size motors you need.

90% of the machines being built here use 380oz motors and G540's, and perform very well. I think you'd be better off with 2010 than with 2510's, but even with 2005's, the machine will be usable. I'm just trying to save you the cost of upgrading later.
While everyone says they don't care how fast their machine is when they're building it, everyone wishes their machine was faster once they start using it.

Will I need the higher ipm for better part-finish?

Depends on what you're cutting. Cutting too slow will result in shorter tool life, but in some materials, cutting slower might give you a better finish. When cutting wood, a good rule of thumb, for maximum tool life, is to cut as fast as possible while maintaining a good surface finish.

[PaulRowntree]

I see what you mean. How about a base set in concrete? And then maybe the OSB on top of the concrete to have something to screw into. How do you think that would work?

I will try getting some dimensions on the model. Any particular you had in mind?

I think you want to find a way to make the frame and supports adjustable and rigid at the same time. Concrete is hard to use in a precise way, although the epoxy/granite thread is interesting (and long!). Some builds here use concrete in the base, but not many. Many people make good straight torsion boxes of MDF, and then use this as their support. If you can make one that is flat, it is an inexpensive route. And much more portable than concrete. As you can see in this forum, steel frames and rail supports are becoming very popular, and epoxy levelling seems to be viable.

For dimensions, I was just wondering about the travels etc, gantry heights, and so on.
Cheers!

[Lynge]

Some dimensions:
The x-rails (blue) are 1500mm SBR25
The I-beam (Y, yellow) are 890mm and the Y-axis SBR16 rails are 770mm
The gantry height nothing (I think?) as the I-beam rests directly on the X-rails.

The Z has a travel of 193mm but will not be able to use most of it in this setup. But I figured that I could make a new base for the machine, or maybe cut a hole in this one, if I ever need to have more height.

The Z uses SBR16 as well.

Should I jump to SBR20 on the Y?

On ballscrews:
I think I will stick with 5mm pitch. I see the sense in what you say Gerry, but I would rather have a machine that is too slow, than one that is too heavy for the motors I have for it.
I would just have bought stronger motors, but as I already have the motors, they will have to do.

Calculated IPM for the lot at 1350mm in length:
1605 - 167ipm
2005 - 208 ipm
2505 - 261 ipm

So it looks like the 2005 is a nice middle ground, but then I have to make custom ballnut housings, or pay the rather steep prices for a ready-made one. Hmm, tough call.

On the base:
I have some 150mm x 150mm I-beam sitting around. I know it is not straight enough, but how about some of that, with some epoxy on top to make it level?
I figure I can set them up against one another and pour the epoxy in one large pool on top of them both. Then, when the epoxy has set, saw it and separate the I-beams again. They should then be the same height, right?

[Phife]

Id be concerned that the I beam you plan to use for the Y is not straight or flat enough.

The way you have the rails mounted is probably the best way for that setup but if there is any variation in the I beam you could get binding and poor accuracy.

[Lynge]

Phife: Yes, that has just struck me as well. I have asked on a local forum for a guy with a mill that can help me get it straight.

But the placing of the y-rails looks fine to you? How about the size, sbr16 vs sbr20 ?

[Phife]

Phife: Yes, that has just struck me as well. I have asked on a local forum for a guy with a mill that can help me get it straight.

But the placing of the y-rails looks fine to you? How about the size, sbr16 vs sbr20 ?

The Y rails are fine where they are placed, on your Z axis you should try to place the rails on the side as when you are routering on your X axis in one direction you are pressing the rails into the blocks which is the strongest direction to take loads, but in the other direction you are pulling the rails out of the blocks which is the weakest direction for those rail to take a load.

As for SBR16 vs 20, I see no reason not to use 20 if you can afford it, better to over engineer IMO, but the load ratings are not that much different.