Looking for advice/concerns on new design

[stangtjk]

I started collecting parts and designing a router in December. I think I've got the design pretty well worked out, just looking for some input before I start building so I can make changes before hand if needed.

Here a some pics of what I have in mind.






Parts I've accumulated so far:
- Linear bearings are rollon 43 series compact rail
- Z-axis is a ball screw linear actuator from IAI with about 8 1/2" of travel
- 4.8:1 belt reduction using 10T and 48T XL pitch pulleys
- 3/4" wide L pitch open ended belts and 12T pulleys to drive X and Y-axis
- 4 IM483H drives w/ 40V PSU
- 44" 8020 45-4590 extrusion for the gantry beam
- 4 parker OS stepper motors (probably will need something else but they were only $50 for the lot and are brand new)

Parts I still need:
- electronics: BOB, motor cables, limit switches...
- router
- bearings for the pulley shafts
- material for the base of the machine
- I'm sure there's more

For the design pictured I'm planning on using 1"x1"x1/8" square tubing as shown backed with a 1/4" plate for the base, the uprights for the gantry are 1/2" thick aluminum plate. Think this will be strong enough? My family owns a small steel supply shop so I have access to whatever steel I want if I need to beef up the design, however I move around a lot and would prefer to keep things as portable as possible. I'm just building the machine for fun and don't think I need really high tolerances however I'd like to make the best machine I can. I'm planning on doing some wood carving mostly but hell if I can teach my dad to run it it might turn into a plasma table for his shop.

Any input is welcome. If you think the design is crap let me know so I can change it.

Thanks,
Tim

[stangtjk]

Here is what I have for the Y and Z axis.

[stangtjk]

You may have noticed the linear actuator in the drawings was not the same as the one I have. I guess the one I picked up is an outdated model and IAI no longer has the cad files for it on their site (if they ever did). I was lazy and just downloaded a similar model but I got bored today and decided to draw up the one I had. I also added some angle to the inside of the gantry uprights to bolt up to the 8020 extrusion. I think I'm done with the modeling, there have been a lot of views but no comments with concerns or advice so I guess there's nothing majorly wrong with the design. Looks good to me anyway. I'm hoping to start building in the next week or two. I'm still undecided on how I'm going to do the work table, might get that worked out tomorrow. Here is some eye candy of the latest revision.

[Jesse B]

I assume you'll have the bottom mounted to a surface?

[basskitcase]

Regarding the 1" steel frame, that is what i used on my router. You can check out the build log here (still a work in progress)

1st build: Bright orange steel framed router

I think everyone probably has a unique definition of ridgidity, but for my purposes if i had to do over, i would either use 2" tube, or double up on the 1"

I have a little flex in my due to only having a single tube thickness on the base of the gantry (which i hope to remedy soon), but realisticly, i think the motors would probably stall before i had a signficant amount of flex (i don't really need exacting tolerances).

[rcbamm]

Hey Tim.

I like your design. Nice job on the 3D design.

I'm now leaning towards the L pitch 12T pulleys. The only thing I'm worried about is the amount of teeth that are going to be in contact with the pulley. I'm worried that underload, the very few 3/8" pitch teeth that are in contact with the 12T pully will have some sort of downside effect on the work it is doing. Because the pulley is so small and so much force is going on only a few teeth. Do you think this is true? I'm definitely going with 1" wide L pitch belt from polybelt.com. But now I'm trying to figure out what size pulleys I'm gonna use to carry the belt on the X and Y axis. I chose a 20T pulley earlier but that would be 7.4" per revolution which would make me have to use a really big reduction drive, which in turn makes it more complex and the price go up. I'm trying to figure out if, a 20T versus a 12T pulley would really make a difference cutting wood and foam.

Again, I'm going with 1" wide L pitch belt because I'm gonna have 11ft of open ended belt on each side of the gantry.

[stangtjk]

rcbamm,
I didn't even consider the tooth contact of the 12T L pitch pulleys, I wanted the smallest pulley I could find so I wouldn't need a large gear reduction as you mentioned. However I really don't think it would be a problem. I imagine it would take a lot more force than any stepper motor I plan to use to cause a properly tensioned belt to slip. I'm using 3/4" wide belt because that's as wide as the pulleys I have will take and they only cost me $15 for all 6 of them. Here is a link to the ebay auction if you want to use 3/4 belts and save some money http://cgi.ebay.com/ws/eBayISAPI.dll...m=380199077491

basskitcase,
The usage of the 1" tube between our designs is quite different so I don't think I'll be running in to the same problem. I could go up to 1 1/4" without changing things much but I'd have to completely redesign everything if I were to use 2".

Jesse,
I'm not sure what exactly you mean, I take it you're wondering about the cutting table? I'm not 100% sure yet but I'm thinking of doing something like this.

[rcbamm]

Well, I think I'm gonna follow in your footsteps. I'm either gonna choose a 12T L pitch pully or a 14tooth to carry my X and Y axis belts. If I'm gonna get the 12T I'm gonna go with your choice in pulleys for a reduction.

What size is your router table gonna be? Also, are you using Autocad?

Oh and how much does your Y and Z axis rail weigh? that setup looks nice and lightweight. Where did you get it from?

[stangtjk]

I just edited that last post, don't know if you saw it, may want to take another look.

The outer dimensions are around 4'x4' and It has a cutting area of 34"x35"X8". I'm using solidworks for the modeling, I have experience with AutoCad, ProE, and ANSYS. I like solidworks the best for modeling, ANSYS is great for analysis but modeling on it is a PITA. Never cared much for AutoCad or ProE. Google sketchup is pretty awesome for freeware.

The Z axis I snagged off ebay for $21.50 + shipping so like $30 LOL. Its an IAI linear actuator. Got really lucky on that one . Its got nsk linear rails and a precision ball screw. All the stuff in that photo for the y and z weight about 35-40lbs total.

[rcbamm]

Wow that actuator was a deal!


For the heck of it. I just bought a lot of 25 of those 3/4" 12T L pitch pulleys off Otterconsignments ebay store for $33.30 shipped. Even if I don't use them for my CNC router, I'll probably end up using them for a future project. When they cost $10 a pop brand new, 25 for $30 is hard to pass up!

I'm kinda wondering now if I can get away with 3/4" wide belt. In my mind I feel safe with 1" wide. I wonder if in the real physical world they differ much.

[rcbamm]

Well shoot you know what. If the 3/4" belt does not hold up for what I'm gonna do, and since I'm getting 25 12T pulleys. I will just leave room on my CNC table to be able to have the option to slap another pulley on each corner to double on the belt. So for right now I think I'm just gonna go with the 3/4" wide belt like you are doing Tim. To keep the cost down, but have the option to upgrade


Well lemme edit this post.

I'm only gonna be saving $45 by using the Ebay 3/4" 12T pulleys (which do not have a hub) and 30 feet of 3/4" wide belt. Benefit for this setup: The option to ad another 3/4" wide belt in the future. $33 for ebay pulleys and 30ft of 3/4" wide belt $73 = $106.

For a $151 I can get 6 x 1" wide 12T L pitch pulleys (which have a hub) and 30ft of 1" wide belt.

I wonder if the single 3/4" wide belt would be just as good as the 1" wide belt, and if the doubled 3/4" wide belt is necessary

[Jesse B]

Jesse,
I'm not sure what exactly you mean, I take it you're wondering about the cutting table? I'm not 100% sure yet but I'm thinking of doing something like this.

That's what I meant. From your design it just looked like it'd be placed on a counter top and the material would be placed there as well. I can see now that you design wasn't finished though