[JohnnyVegas]

I have been designing a smaller table top machine the past few weeks. I've been trying to keep it simple with most parts available at Home Depot and Lowe's. That's why this build is called the "Home DeBot".

I would appreciate anyone's opinions or ideas on the design as I go along.

For the most part this is the complete design. I still must add various fasteners around the machine but those can be added along the way. I'm mainly concerned with the idea and function of the design. I'm looking at a cutting area of 12-14" x 24-26". The overall foot print is 38"x24" and all the electronics and bit holders will be incorporated on the machine. The plan is to place them on the "dead" area on the rear of the table surface. The electronics are all ready built using the PicStep design. I have a build log on that all ready. http://www.cnczone.com/forums/picste...minmo_bob.html. I'm using 280+oz steppers and the machine is using a 3/1 XL gears on 2 of the axes in the pictures here. I have to incorporate the gear on the Y axis next. I can't do 4 steppers as I only have 3 PicSteps built and do not feel like building a forth. The router is a Bosch Colt and the lead screws are precision acme 10 TPI. I have an acme tap so I will be making my own anti-backlash nuts.

Here is the design at this point. I will be updating the design as I go along.

[ger21]

It looks pretty cool, but those shafts are going to flex like wet noodles. And the 3/4" sides aren't going to be strong enough, either.

[JohnnyVegas]

It looks pretty cool, but those shafts are going to flex like wet noodles. And the 3/4" sides aren't going to be strong enough, either.

Interesting. According to my math they should be fine. What size would you suggest? 3/4" shafting? They are 440C stainless steel.

I see a lot of people with the 3/4" sides on larger machines but maybe your right. I'll beef it up more.

[JohnnyVegas]

McMaster sells the XL belts is standard lengths and the original pulley system on the front was requiring a 43.44" belt. Well... McMaster sells a 42" and then jumps to a 45". I updated the pulley system to make sure a 45" belt will work.

Also included a shot of the back of the machine. I was going to keep all the pulleys and gears on the rear but I like the idea of seeing the gears turning on the front of the machine. The gears are mounted on the ends of turned down Acme screws and drives both X axis shafts.

[ger21]

Interesting. According to my math they should be fine. What size would you suggest? 3/4" shafting? They are 440C stainless steel.

What size are they, 1/2". There used to be a video on here of a similar design using 1/2" shafts. One finger pushing near the tool could easily get .25" or more deflection. For the Z, they should be OK, if they're not too long. I use 18" long 3/4" SS for my Z axis and it doesn't have any flex.

Are the ones on the gantry about 20"?

[beermkr]

Do you foresee any stretch in your belts. Seems that the combination of two stretchable links to drive the second acme screw may cause some racking.

R/

[JohnnyVegas]

What size are they, 1/2". There used to be a video on here of a similar design using 1/2" shafts. One finger pushing near the tool could easily get .25" or more deflection. For the Z, they should be OK, if they're not too long. I use 18" long 3/4" SS for my Z axis and it doesn't have any flex.

Are the ones on the gantry about 20"?

Perfect. I'm going to upgrade the model to 3/4" SS. May take a little work.
The Z is only 12" tall so I think that will be fine. The Y rods are about 36" long. The X gantry rods are about 24"

[JohnnyVegas]

Do you foresee any stretch in your belts. Seems that the combination of two stretchable links to drive the second acme screw may cause some racking.

R/

No. They may need to be replaced way down the line (similar to a cars timing belt) but they are reinforced belts so they should not stretch at all. The tension pulleys are adjustable so I assume that they should work nicely.

[ger21]

I'm using 280+oz steppers and the machine is using a 3/1 XL gears on 2 of the axes in the pictures here. I have to incorporate the gear on the Y axis next. I can't do 4 steppers as I only have 3 PicSteps built and do not feel like building a forth. The router is a Bosch Colt and the lead screws are precision acme 10 TPI.

You're 3:1 gearing is going to actually cause you to go slower, as the steppers will need to spin 3 times than direct drive to get the same speed. Torque drops off rapidly as rpm's increase, so this is a bad idea. It's OK if you need more torque and not faster speeds, but not for a router.

If you insist on 1/2-10, then gear it 1:2 or even 1:4. Typically, the best balance of precision and speed from an acme screw is .25"-.5" of travel per motor revolution.

A better option would be 1/2-8 2 start or 4 start, or 1/2-10 2 start or 5 start. 2 start screws should be almost twice as efficient as 1/2-10, and 4 or 5 start even more efficient. This can mean up to 30% more force using the same motor.

[ger21]

You may still get to much flex at 36" with 3/4". Even the 24" may be pushing it.

[JohnnyVegas]

@Ger I think your right. I should double any calculations. It's hard to know exact forces when the machine is cutting.

Upgraded to 1" hardened SS on X and Y. I will possibly upgrade the Z to 3/4" but not sure if it's necessary. With this upgrade the machine would effectively need to flex 2" of steel over a bridge of 8" (effective -28" span). I should be able to do pull-ups on them.

Updated model.

[JohnnyVegas]

You're 3:1 gearing is going to actually cause you to go slower, as the steppers will need to spin 3 times than direct drive to get the same speed. Torque drops off rapidly as rpm's increase, so this is a bad idea. It's OK if you need more torque and not faster speeds, but not for a router.

If you insist on 1/2-10, then gear it 1:2 or even 1:4. Typically, the best balance of precision and speed from an acme screw is .25"-.5" of travel per motor revolution.

A better option would be 1/2-8 2 start or 4 start, or 1/2-10 2 start or 5 start. 2 start screws should be almost twice as efficient as 1/2-10, and 4 or 5 start even more efficient. This can mean up to 30% more force using the same motor.

i have the screws all ready so that will be a future upgrade. bummer. but great info.

The gearing can be changed easily. So If .25" or .5" per revolution is the goal my gearing is backwards. I should be doing a 1:2.5 or a 1:5. That's why I posted here and choose to use gears.

[MRM RCModels]

I was wondering when you were going to start building a machine! The design looks good. What do you plan on cutting? Unsupported rails are a good choice for cutting foam and light cuts in mdf. Might want to look into a set of supported rails if you're going to do any harder materials. Just my 0.02. Looks good though.

MRM

[JohnnyVegas]

I was wondering when you were going to start building a machine! The design looks good. What do you plan on cutting? Unsupported rails are a good choice for cutting foam and light cuts in mdf. Might want to look into a set of supported rails if you're going to do any harder materials. Just my 0.02. Looks good though.

MRM

Not sure. Slow cuts in MDF / plastics / PCB's really. Not interested in speed with this model.

I have V groove bearings coming in soon and am now considering using them on this. With the cost of 1" alloy round this design is slowly becoming not-so cost effective. Not sure if I should continue with this design or alter the linear design elements.

I saw on ebay I can get some supported rails @ 39" + 4 pillow blocks for about 130.00 shipped from China. At that price I may just go that route.

The "Home De-Bot" would then become the "eBot"!

[JohnnyVegas]

Reworking the model this week. The last model will be shrunk down a little to work on PCB's maybe. I'm interested in seeing it work now so I will be cutting it too.

Home Debot v2.0 will be coming shortly.

[JohnnyVegas]

There have been some improvements and changes in the design. The cart has had a major re-work. Still working out the very fine details. I will be cutting this first before cutting the machine to ensure it works nicely. I keep going back and forth with the idea of making a larger machine then use it to cut the table-top machine. The larger machine would be more of a 2'x4', 3'x4' or 4'x4'

Here is a shot of my progress so far.

[ger21]

That looks pretty cool. Not sure if I like the Z stepper hanging out like that though. With 10 lbs hanging from it, it will sag over time. One way to make it stiffer is to laminate layers of 1/4" MDF, as many as you need to get that thickness. It'll be much more dense, harder, and stiffer.

Can you post larger pics. I hate the ones that size where you can only get a rough idea of what your'e looking at, but can't really see any details.

[JohnnyVegas]

That looks pretty cool. Not sure if I like the Z stepper hanging out like that though. With 10 lbs hanging from it, it will sag over time. One way to make it stiffer is to laminate layers of 1/4" MDF, as many as you need to get that thickness. It'll be much more dense, harder, and stiffer.

Can you post larger pics. I hate the ones that size where you can only get a rough idea of what your'e looking at, but can't really see any details.

The Z is (2) .75" Pieces laminated but the design does allow for a centered Z if I needed o go that route.

[JohnnyVegas]

Did some more work today. Almost complete. 90% of the fasteners are in now. I added a 2 1/4" vacuum hose holder to the cart. Right now I'm working on a grinding jig to grind 45 degree angles in steel/ Aluminum angle. I know there is a "skate" jig floating out there but would rather rig up something myself.

I have a million ideas to add but would rather start cutting this out soon to be sure it works well in real life. If it works I can always use it to cut alterations.

[mmcp42]

[iijit.question]
what's the second stepper motor for
the one on the top is, I gues, Z-drive
I can see the spindle motor
but it looks like there's another stepper there?
[/iijit.question]