8020/cncrouterparts.com/rackandpinion/suggestions welcome

[lunchtrayrider]

I've started/nearly finished designing (wishful right?) a build. I've already built two small mdf routers but am looking for something a little beefier. Here are a few images. I would love any feedback relating to the interconnection of the 8020 as I have no experience with this. questions or comments very welcome.

The design concepts are as follows:

I wanted an extremely efficient envelope. so I tried to make everything overhang and interlock as best I could. The cuttable area is 22.5 x 34.5 so I should have no problem doing 22 x 34 pieces. The primary use will probably be topography for my architecture models. I also wanted to keep the cost as low as possible but am not willing to skimp (i still want a gecko g540 and ahren's sweet motors but want to keep my cost under $2000 for the initial build.) A lot of my dimensions are just bigger then what ahren and nate offer for sale on their websites, but i live very close (same city) as discount steel so I can get my steel for rails pretty cheap. I wanted to use the rack and pinion drives because a lot of machining will be out of rigid insulation foam. it cuts pretty fast, so it like to speed through it accordingly. Those are my basic goals and concepts. thanks for any feedback.

the first three images are the obvious shots. the fourth shows how I am lining up the y-carriage and the y gantry leg. the 1/4" steel plate is actually designed to be notched here. The upper y-carriage is ahren's long bearing block which is two inches wider the the short bearing block that is on the bottom of the y-carriage. this allows a two inch overhang on the top saving me 4 inches in total width. i also slide the y gantry rail one 'notch' back in the 1545 from the front. i can add gusset plates on the backside to strengthen the corner in this position. I considered moving the y gantry rail all the way to the back of the y-gantry legs to better align the router with the y-gantry leg bearings but then the z-carriage bearing blocks interfere with the y-legs and I lose my width advantage. I would also like to be able to have the router reach past the end of the table to do finger joints in wood that I could clamp out there. stuff in the background is greyed out. thanks again.


-aaron

[ahren]

Hi Aaron,
Looks like a clever design and use of space. I'm not sure you'll see too much speed benefit from the R&P over 5 start screws for a machine this small -- it does take time for any mechanical system to accelerate. Still, it should be somewhat faster for larger pieces.

It looks like you have a good handle on things -- really nice work in CAD. My only advice is that if you think you want to build parts that are 22 x 34, you go larger by at least 4 inches, and preferrably 6. Keep in mind that you need to take into account cutter offsets. Additionally, it's annoying while you're jogging around to keep running into limits, and this will happen often if you're trying to locate off the edge of stock for a large part.

Best regards,

Ahren
www.cncrouterparts.com

[CarveOne]

Originally Posted by lunchtrayrider I've started/nearly finished designing (wishful right?) a build. I've already built two small mdf routers but am looking for something a little beefier. Here are a few images. I would love any feedback relating to the interconnection of the 8020 as I have no experience with this. questions or comments very welcome. The design concepts are as follows: I wanted an extremely efficient envelope. so I tried to make everything overhang and interlock as best I could. The cuttable area is 22.5 x 34.5 so I should have no problem doing 22 x 34 pieces. The primary use will probably be topography for my architecture models. I also wanted to keep the cost as low as possible but am not willing to skimp (i still want a gecko g540 and ahren's sweet motors but want to keep my cost under $2000 for the initial build.) A lot of my dimensions are just bigger then what ahren and nate offer for sale on their websites, but i live very close (same city) as discount steel so I can get my steel for rails pretty cheap. I wanted to use the rack and pinion drives because a lot of machining will be out of rigid insulation foam. it cuts pretty fast, so it like to speed through it accordingly. Those are my basic goals and concepts. thanks for any feedback. the first three images are the obvious shots. the fourth shows how I am lining up the y-carriage and the y gantry leg. the 1/4" steel plate is actually designed to be notched here. The upper y-carriage is ahren's long bearing block which is two inches wider the the short bearing block that is on the bottom of the y-carriage. this allows a two inch overhang on the top saving me 4 inches in total width. i also slide the y gantry rail one 'notch' back in the 1545 from the front. i can add gusset plates on the backside to strengthen the corner in this position. I considered moving the y gantry rail all the way to the back of the y-gantry legs to better align the router with the y-gantry leg bearings but then the z-carriage bearing blocks interfere with the y-legs and I lose my width advantage. I would also like to be able to have the router reach past the end of the table to do finger joints in wood that I could clamp out there. stuff in the background is greyed out. thanks again. -aaron

Two issues I see in the end view drawing that I think should be pointed out for consideration:

1 - The rails are below the table top and dust/debris will quickly pile up on them if nothing is done to prevent it.

2- The carriages seem to have no means to keep them from spreading apart other than the gantry vertical supports being fairly stiff. My question is whether the extrusions can be counted on to prevent binding and misalignment. The pinions running in the racks may or may not help keep the carriages running on track. The bearings that run on the edges of the rails may develop gaps and not touch the rails.

CarveOne

[ahren]

CarveOne,

Good feedback. I think with a dual drive system, the spreading of the gantry will not be a big deal. If a strong butt joint connection is used for the gantry, things should pull together pretty tightly, and with long bolts going through the carriage into the gantry uprights, it should be a pretty stout connection. It might be worth reversing the pivot point on the R&P drives. The pivot point shoulder bolt obscures one of the mounting holes through the carriages, and it would be nice to run three bolts into the gantry upright.

As for the horizontal rails, it might be worth mounting some sort of wiper system to the uprights -- this is not too hard, and has worked well for others. The horizontal configuration is nice for making adjustments for final fit / square / parallelness.

Best regards,

Ahren
www.cncrouterparts.com

[lunchtrayrider]

thanks for the replys guys,

I guess size wise I really want a 4'x4' to at least cut half sheets. But right now this is literally something that needs to fit under my desk at school. I think i forgot to mention it but another reason I really would like to do the rack and pinion so that I can transfer as much of the good stuff as possible. 8020 probably can always be repurposed and the z axis will most likely stay the same. so I figure that with the rack and pinion im out $65 for rack and $70 for steel when i make it bigger.

also, most of the work will be shaping of the surface of materials. the largest bit I really plan on using will be 1/4" even then if it is too close to the limits i'll make the workpiece into smaller chunks. the size is something i'll have to live with for now.


carveone's comment about the legs is probably my biggest concern right now. I'm not exactly sure that the 8020 is up to it like that. I took a measurement just now and where I can attach a gusset plate on the backside of the gantry down to the top of the steel rail gives me a torque arm of around 7.25 inches. do you think the 1545 can hold up to that?


-aaron

[ahren]

I think you will be fine. Since you are driving it from both sides, there is really very little load trying to "spread" the gantry. You can input a heavy cutting load into 8020's deflection calculator to get a numerical value for deflection (something like 50 lbs). Realistically you'll never see this if you are cutting foam, and the 8020 is pretty stiff. That span isn't much worse than your z-axis.

Ahren
www.cncrouterparts.com

[CarveOne]

Originally Posted by lunchtrayrider thanks for the replys guys, I guess size wise I really want a 4'x4' to at least cut half sheets. But right now this is literally something that needs to fit under my desk at school. I think i forgot to mention it but another reason I really would like to do the rack and pinion so that I can transfer as much of the good stuff as possible. 8020 probably can always be repurposed and the z axis will most likely stay the same. so I figure that with the rack and pinion im out $65 for rack and $70 for steel when i make it bigger. also, most of the work will be shaping of the surface of materials. the largest bit I really plan on using will be 1/4" even then if it is too close to the limits i'll make the workpiece into smaller chunks. the size is something i'll have to live with for now. carveone's comment about the legs is probably my biggest concern right now. I'm not exactly sure that the 8020 is up to it like that. I took a measurement just now and where I can attach a gusset plate on the backside of the gantry down to the top of the steel rail gives me a torque arm of around 7.25 inches. do you think the 1545 can hold up to that? -aaron

The spreading issue may not be real, but it seemed worth pointing out that it will be worth investigating and have a backup plan worked out just in case. If it is not a real issue and yours works fine, then others may follow your lead.

I correctly guessed that you went with the pinion drives with possible future plans to move them to a larger machine. I did the same.

CarveOne

[lunchtrayrider]

thanks for the feedback, i'm going to model some more to show what i'm talking about better. the problem is that if the spreading is a real issue then im not sure what a good backup plan would be. I really want to avoid having the cross piece under the table for various reasons, most of those being that this won't have a permanent spot while im at school. im going to work on it and design some backup plans.

[CarveOne]

Originally Posted by lunchtrayrider thanks for the replys guys, I guess size wise I really want a 4'x4' to at least cut half sheets. But right now this is literally something that needs to fit under my desk at school. I think i forgot to mention it but another reason I really would like to do the rack and pinion so that I can transfer as much of the good stuff as possible. 8020 probably can always be repurposed and the z axis will most likely stay the same. so I figure that with the rack and pinion im out $65 for rack and $70 for steel when i make it bigger. also, most of the work will be shaping of the surface of materials. the largest bit I really plan on using will be 1/4" even then if it is too close to the limits i'll make the workpiece into smaller chunks. the size is something i'll have to live with for now. carveone's comment about the legs is probably my biggest concern right now. I'm not exactly sure that the 8020 is up to it like that. I took a measurement just now and where I can attach a gusset plate on the backside of the gantry down to the top of the steel rail gives me a torque arm of around 7.25 inches. do you think the 1545 can hold up to that? -aaron

When lengthening the machine, you can butt join the original racks to another pair of racks. It isn't too difficult, and you can easily align them.

CarveOne

[lunchtrayrider]

carveone-
i though about joining racks later, but i'm going to get the cheap mcmaster ones now and get nicer ones later on. i'm posting some more images. im not sure how much has actually changed, but i picked up a hitachi m12vc router so I could nail down some dimensions. Technocnc has some 6" 1/4" spiral cutters for cheap so I designed around that bit being able to cut 6" deep foam. (worst case scenario kind of thing, I ended up with 9" of z travel to make that happen.) i've got 6.25" of clearance under the gantry. I can get more space by changing the spoil board if needed. I also changed the y rail to 6" wide plate instead of 4". it gives me some options for reinforcing the gantry if need be this way. I believe that there is enough room on the backside of the gantry to make up any stiffness needed but i doubt it is needed at this point. (at least for what I plan on cutting.) I also modified what ahren shows on his site for a z-axis drive assembly. I removed the second coupler and tool steel shaft. i've decided to do this like sieg's machine in ahren's examples on his site show. see here:

YouTube- Cnc Overview 4 - z axis and drive screw

YouTube- Cnc Overview 4 - z axis and drive screw

this is all for now.

[CarveOne]

Your biggest problem with a 6" cutter will be run-out and vibration. At some rpm it will start vibrating and that will shorten router bearing life if it continues for long periods of cutting.

The company that makes the RenShape molds I use has problems with them in a 5Hp spindle on a 5x10 ShopBot. If you are cutting softer foam it won't have the kind of side loads on the cutter that they encounter, but the cutter can vibrate when just running in air if the router collet has any run-out at all. All you can do is try it and see what you get.

The 6" rail is probably a good idea. I've been thinking of doing it on my gantry as well.

CarveOne

[jsheerin]

I use Ahren's carriages on the outside only of my gantry legs and have no problems with spreading. This is on a router with a 49"x49" cutting area. However I have a bit different mounting method for them than what you've designed. It looks like my method would not work with Ahren's R&P setup though. I'd also second the suggestion to do something about covering your rails to reduce material buildup. I didn't do this and it's a constant battle to keep crap off the rails. My z axis has stalled several times due to this. I'm about to redo my entire router to solve this problem.

Pic: