[Tkamsker]

Hi
nice design i work on similar one
I understand the X axis Extrusion Alu but why don't you put the X axes spindle "higher" i expect you will get a lot of load on that little driving piece.
if you look on an force parallelogram ,..
i would do anything tho get the x spindle as close as possible to the cutting point of the spindle.
thats why i would avoid in y axis the "fat" extrusion parts
Why don't you simply use 2 20mm steel rods where you can also use them for the y ball bearings

is your target to cut steel with that machine ?
or why do you have this heavy rails in y axis ?
just my 5 cents
thomas

[LeeWay]

That is shaping up to be a nice design. Looking pretty good. As mentioned, you could save some by using steel for the base. Angle iron would be a good cheap choice. Structurally pretty strong as well. You loose the benefit of T-slots for the table base itself, but drilling a few holes in angle is easy enough. Then you could easily mount the table base from below where you would have to use expensive hardware with the 80/20.

Consider loosing the risers on the Y trucks to make clearance for the Y screw.
I better method is to use flat bar (steel or aluminum) under the entire rail and mount the Z axis directly to the trucks. This also gives extra support the the gantry beam.
That is about all I can see that I would think on.

Of course there are various ways to attach both the screw and the rails for your Y axis, but I think you hit on the cleanest strongest of the all with the screw between the rails all on one side.

Oh and just to be clear, I'm calling the Y axis as the moving beam and X is the high rail table.

[dmalicky]

Another nice clean design. You're good at this. It's definitely stiffer to put the X rails above the table. I'd put them about half as high, for stiffness and easier access to the table. It's not difficult to make the risers stiff, especially if they are only ~3" tall.

On the Y rail vertical spacing, yes, 4.5" is fine for profile bearings cutting wood. I agree that a single piece gantry extrusion is better than something built-up.
Maybe this is a preliminary design, but the one important change I'd suggest is to use 2 bearing blocks per rail for the Y rails. With 1 bearing/rail, lateral forces on the cutter would cause the Y car to rotate. Even the "long bearing blocks" are not nearly as stiff as 2 bearing blocks spaced apart (these are a source of flex on our flexy K2). Normally, the 4 Y axis bearing blocks are arranged in a ~square pattern (when viewed along the X direction).

Yes, Y car spacers are usually needed to get the ballscrew between the Y rails. Solid aluminum is good. Or if you prefer it on top like the last image, that is likely fine for wood, since the profile rails are so stiff (if doing that, design the bracket so it is stiff in the screw direction).

If using a commmercial linear stage for Z, just make sure it has no slop in the bearings and ballscrew; many of them do.

You probably know this: a flexible coupler is needed between each motor and its ballscrew (to absorb misalignment).

The bracing under the table looks very stout. If that gets expensive, you could change to regular rect or square tubing. Either steel or alum would be much less $ than 8020. Alum is easy to cut and drill. (Angle iron is hot rolled w/o any cold finish, so it tends to not be as straight, but over 2' it may be fine, too.)

[wizard]

This is looking very nice!

As has already been pointed out you should really use more than one bearing block for Y axis saddle support. The Z might need a rethink in that regard too. When it comes to profile rails you have lots of options out there including rather wide rail stock with corresponding bearing blocks. However more conventional rails properly positioned with the saddles suitably installed are fine choices. So in your design I'd seriously consider more bearing blocks on the Y axis and look again at the Z axis.

It should be noted that the wider saddles and additional bearing blocks would force you to use longer rails on the Y axis beam and probably a longer beam. This wouldn't impact your overall design.

I mentioned this in another thread but having the ability to run the cutting tool off one end of the machine can be very useful in a moving gantry router as it can allow for the machining the end of stock. I'm not sure if this is useful to you, but considering some of the usage you have described it might be something worth designing in. This implies that the whole machine is mounted such that you can actually realize the vertical usage and provide for the required work holding. You may have to tweak the design a bit but it may well be worth it if you need to cut tenons, box joints and other features on medium length stock.

[LeeWay]

I overlooked that he was only using 1 truck per rail. I though he might be doing minimalistic in the drawing to save time. I do see where he has the bearing centered on the Z stage now though, so yes, by all means, use 4 trucks.

[bluntend]

Thanks again for the input everyone. Here's another tweak, taking some of the suggestions into consideration. Mainly, using square steel tube for the cross members underneath, using spacers under the Y-axis rails instead of on the blocks, and adding a second block to each Y-axis rail.

Attachment 217254 Attachment 217256 Attachment 217258 Attachment 217260

Tkamsker, I'm afraid I don't follow what you're trying to say. I could be misunderstanding what you wrote, but I think you're using the word "spindle" to refer to more than one thing. I'm also not clear what you mean by "that little driving piece". Are you referring to the X-axis ball screws and the steel bar that joins them to the Y-axis gantry above?

Wizard, I don't think I'll have an immediate need for the router to run beyond the table for tenoning etc, but you're right that it may be a good idea to plan for it just in case that changes down the line. I think I would be able to adapt the existing design later by putting in a shorter table bed and moving the end aluminum cross member (the one that goes in the y-direction) in, shortening the length of the table. This would allow the router to extend beyond the table surface. It's one of the nice things about the slots in extruded aluminum construction I suppose.


dmalicky, your point about avoiding slop in commercial linear stage is something I didn't think of. I assumed that if I went with a good name (THK, Hiwin, etc) that there wouldn't be any more slop than found in the rails and trucks I'm using on the X and Y axis. Is this a poor assumption to make? It could be the kind of thing a newb like me ends up regretting...

I do know the motors will all need flexible couplers, I just didn't bother putting them in the sketchup file. =)

[wizard]

Thanks again for the input everyone. Here's another tweak, taking some of the suggestions into consideration. Mainly, using square steel tube for the cross members underneath, using spacers under the Y-axis rails instead of on the blocks, and adding a second block to each Y-axis rail.

The steel cross members are nice and should save you a bit of money. I'm not sure what size you are looking at but 2" square tubing can be had pretty cheap in full lengths.

However there is not thing I don't like. I'd rather see those cross members extend out far enough to allow the installation of reinforcing angle brackets. This to help stabilize the X axis rails. This is probably the opposite of what others have indicated but I offer up this suggest out of my reluctance to rely too much on extruded aluminum structures.

I'd also consider gussets to keep the frame from racking. In other words once square you want to make sure the frame stays square.

Tkamsker, I'm afraid I don't follow what you're trying to say. I could be misunderstanding what you wrote, but I think you're using the word "spindle" to refer to more than one thing. I'm also not clear what you mean by "that little driving piece". Are you referring to the X-axis ball screws and the steel bar that joins them to the Y-axis gantry above?

Wizard, I don't think I'll have an immediate need for the router to run beyond the table for tenoning etc, but you're right that it may be a good idea to plan for it just in case that changes down the line.

For some reason I thought you where into musical instruments. Now I haven't built any musical instruments at all, so maybe I'm wrong, but I was thinking tenons or like structures existed on the necks of guitars and the like. From the standpoint of setup it would be easier to do the end work at the end of the machine. I've seen examples where guys have a section of the table that is removable to allow them work on pieces mounted vertically but it doesn't look all that human friendly.

I think I would be able to adapt the existing design later by putting in a shorter table bed and moving the end aluminum cross member (the one that goes in the y-direction) in, shortening the length of the table. This would allow the router to extend beyond the table surface. It's one of the nice things about the slots in extruded aluminum construction I suppose.

Depending upon what T slot system you use and the connection method it might not be all that easy to move things around in the future. Since the manufactures often support multiple methods of connecting the extrusions you need to make sure your selected method is workable.

dmalicky, your point about avoiding slop in commercial linear stage is something I didn't think of. I assumed that if I went with a good name (THK, Hiwin, etc) that there wouldn't be any more slop than found in the rails and trucks I'm using on the X and Y axis. Is this a poor assumption to make? It could be the kind of thing a newb like me ends up regretting...

There are so many different types of automation stages to choose from that it is worth mentioning that many aren't suitable for machine tool use. Likewise many are indeed very suitable, it is a case of buyer be aware.

I do know the motors will all need flexible couplers, I just didn't bother putting them in the sketchup file. =)

Yeah a sketch is sometimes seen as the final word.

[Tkamsker]

Hi,
sorry i was too short probably (coming from roaming at holidays )
so what i tried to say is there is an Arm between the cutting of your spindle (40mm Motor )and the y axis
there you will get an huge momentum (or more than necessary )
think of if the Z axis i far extended and you start to cut in the middle of y travel it will add all tolerances and be shaky.
Look at the foot of my router (i had problem with my tool changer ,.. ) there you can see 2 thick steel bars are the y axis with stabilize the whole thing
just an idea
thomas
thomas