New design for critiquing

[RakmUp]

I have been designing my machine for many years and have decided to get off the pot, build it and make some parts. This design represents some of what I have read lately and what will make a very workable setup for the operator..me.
Many of you here are experts at this and I am hoping to tap some of your knowledge before I commit to cutting and welding.
The frame is all 2x2 steel tube, .125" wall, welded with linear ways and ball screws on 3-axis. The 4th axis is the A on the lathe portion. The cross rail will be channel iron 7" x 2" x .210"
I know the design is not typical in that the Y (approx 4') is wider than the X (approx 2') but it makes for a nice setup. I am torn between the needs to drive the X with 1 or 2 screws. Is this something that can wait to test pull the gantry to see how hard it pulls and if it wants to bind up if pulled from the center. Can I use 2 motors for the X rather than using a belt drive and share the X axis signal?
I plan to use Geckos and have yet to determine the size of motors I will need. I found out my old Ah-ha system is dead so I need all new drives anyway.
Please let me know if you see any major problems ....other than the heavy duty Z motor mount and the cross tie for the X.

Any constructive (or funny) comments are most welcome.

Regards,
Chuck

[Hobbiest]

Custom pool cues huh? I love to play pool, have been playing pretty seriously for about 8 years now, but have never had a decent cue of my own. I have thought about making a machine for cues...not that I want to make them ofcourse, just the machine! A few questions. What are you planning to use for bearings? What size rods for the ways? what is the travel? Why do you need to have 4 axis {a machine like this usually has only three, X(the longest axis), Z, A}? Why steel (I am a steel fabricator myself just curious)? Other than that it looks good.

[RakmUp]

Custom pool cues huh? I love to play pool, have been playing pretty seriously for about 8 years now, but have never had a decent cue of my own. I have thought about making a machine for cues...not that I want to make them ofcourse, just the machine!

A dead giveaway eh? Great game though, you have to admit!

A few questions. What are you planning to use for bearings? What size rods for the ways? The ball screw I have is only 5/8" but I am scouring E-Bay for any great deals.

I have some Thomson pillow block style linear bearings on 1" shafting.

what is the travel?

X=24" Y=36" Z=6"

Why do you need to have 4 axis {a machine like this usually has only three, X(the longest axis), Z, A}?

I originally designed this like that but realized adding a bit of size would open other possibilities for relatively little more cash. I would like to be able to make furniture spindles that twist and possibly gun stocks as well. Too many cool things really and I am sure it will be too small shortly after I get it running.

Why steel (I am a steel fabricator myself just curious)? Other than that it looks good.

I know people that can build this like this for me for a whole lot less than I can build in aluminum extrusions plus the added strength will allow me more opportunities as well.


Thanks,
Chuck

[Hobbiest]

I originally designed this like that but realized adding a bit of size would open other possibilities for relatively little more cash. I would like to be able to make furniture spindles that twist and possibly gun stocks as well. Too many cool things really and I am sure it will be too small shortly after I get it running.

Spirals can be made on a three axis (x,y,a) machine, because the a rotates as the spindle moves up and down/left and right. Ofcourse...having the x would make it possible to do some standard 3 axis stuff too.

Actually, it was the design of the machine that first tipped me off to your vocation, and then I looked at your name again. You got any photos of your work?

[RakmUp]

Ofcourse...having the x would make it possible to do some standard 3 axis stuff too.

Actually, it was the design of the machine that first tipped me off to your vocation, and then I looked at your name again. You got any photos of your work?

Exactly...other 3-axis stuff...lots of it.

my work?.....you've seen it...just a machine design so far...your signature says it all with me so far. I have been playing the game and actually collecting others work because of the beauty and craftsmanship and have been a wannabe cue maker for too long now. I know most people would say to start out fixing tips and things but that really doesn't interest me. Maybe I'll be one of those that don't last with this but I have a lot of motivation to finally get started and once I start I generally do pretty good. It will be fun none the less.

[RakmUp]

I was about ready to get this fabrication started when I noticed a problem.
I have re-designed this a bit to drive the y-axis with a center motor and 1 timing belt that connects 2 screws, 1 each side near the bearings. The timing belts available for the required length (125") are only available in 2" widths. That seems extreme to me plus I already have the smaller pulleys. The machine will be 52" wide.
Would I be better off using 2 seperate belts, 1 to each side with a double pulley in the middle or should I use 2 motors, one mounted on each side and slave them together? I know Mach 2/3 can handle that but is it a hassle?
I assume you guys have seen both options and 1 is most likely better.

Second question:
The lathe portion of this will be driven by a 3/4 hp dc motor. I also have to have a stepper/servo motor to control the spindle as well. Can I simply double up on the pulleys or will the driving DC motor hurt the idle stepper/servo? Is there single motor solution for this?

Any thoughts are appreciated.

Thanks,

Chuck

[ESjaavik]

@Chuck: Very nice design!
What I would do different is to reverse the gantry so the most sturdy part is close to the lathe headstock. This because when you mill a long part, the part itself will be the one that is determining the stiffness. When it is short the part will be stiff. If you have the sturdiest part close to the headstock this makes it the whole operation stiffer.

Then I would make the center height of the lathe larger. If you want to mill gun stocks axe handles or the like, you will want more swing.

Damn! Your idea is a lot better than mine: putting the lathe on the mill table. I've never seen it done like that. Is there a commercial machine built like that?

You should not drive a stepper up to very high revs like you indicate. You can use a dog clutch. When using the lathe spindle indexed engage the stepper with the dog clutch. When running high speed, disengage the clutch to avoid overrevving the stepper (or low speed servo). Or if the ratio high/low is not too large, use a servo to drive the lathe spindle.

And I would use linear slides for the mill part. That design has a lot of possible uses, don't limit it by using parts that makes it wobbly. The base structure looks good.

[RakmUp]

@Chuck: Very nice design!

Thank you!

What I would do different is to reverse the gantry so the most sturdy part is close to the lathe headstock. This because when you mill a long part, the part itself will be the one that is determining the stiffness. When it is short the part will be stiff. If you have the sturdiest part close to the headstock this makes it the whole operation stiffer.

Actually the design has changed as this is my first draft at design. Like I said, I will be driving this from both sides now so I do not have a long gantry side at all. I really did not want to deal with the racking that probably would have occurred on this design. Both sides are the same now.

Then I would make the center height of the lathe larger. If you want to mill gun stocks axe handles or the like, you will want more swing.

Done, I should have around 8" of swing but the cutter will only go up and over about 6" depending on the tool length.

Damn! Your idea is a lot better than mine: putting the lathe on the mill table. I've never seen it done like that. Is there a commercial machine built like that?

I have not seen one if there is, but it looks practical for my applications. I just hope it pans out.

You should not drive a stepper up to very high revs like you indicate. You can use a dog clutch. When using the lathe spindle indexed engage the stepper with the dog clutch. When running high speed, disengage the clutch to avoid overrevving the stepper (or low speed servo). Or if the ratio high/low is not too large, use a servo to drive the lathe spindle.

Thank you, that is what I thought. I don't think I should have much need for real high rpm turning but would prefer to have the option. I have another wood lathe if the need be.

And I would use linear slides for the mill part. That design has a lot of possible uses, don't limit it by using parts that makes it wobbly. The base structure looks good.

OK, I don't get this. This will be all linear slides. What do you see that you don't like?

Thanks for the reply.

Chuck

[RakmUp]

Just threw this model together so you can see the most current design.
Since posting last, I have decided to go with the 2 motors for the Y-axis and slave them in Mach 2/3.

[ESjaavik]

If you use slaved servos, cross connect the following error outputs to the other drive's error input. If they get too much out of sync they could easily pull your machine out of alignment. I've thought of using slaved servos myself, and would make a supervisory circuit that would disable the drives if they get out of synchronization. If you aim for a decent acceleration, the forces of these motors acting asynchronously will be quite large.

Another solution might be to make a deliberate weakened connection of the gantry to the pads driven by the spindles. Like a mechanical fuse that will let go if the forces is above a certain point.

How do you do when milling in the center of a queue, will there be a following steady on the lathe slide to support it?

In your first drawing the slides looked like rods only supported at the ends, but the last drawing show them connected to the base structure along the full length.

[RakmUp]

How do you do when milling in the center of a queue, will there be a following steady on the lathe slide to support it?

I am going to find out more about this slave business. That is why I am writing here anyway. I appreciate your thoughts. I am not an electrician so you lost me on the fix.
I would think if I use a good system and good motors, that should solve most of the possible problems. There have to be other people doing this without a large problem or it would not have been developed into the software. IMHO

As far as milling the center of the cues, I believe you go for very little tool pressure and unsupported but in some cases you would add some support, maybe not traveling support, just rolling support. The tooling used for most inlays is very small and is run at very high rpm's. To cut the taper, you use a saw blade type cutter with many teeth on the side of the cue and rotate the cue slowly as you traverse the length. This also minimizes the tool pressure and leaves the cue smooth enough for just light sanding to finish.

[RakmUp]

Finally some pictures of the fab. At least it is coming along...maybe slowly but....

This is heavier than I anticipated (not a bad thing I guess), The vendor used heavier wall tubing than I spec'd because he had it in stock for cheap.

Currently, most of it is machined and waiting some final drilling op's.