Need Help!- Linear motion, and frame considerations

[tkubic]

My first router I built was the smaller 12x12 solsyva. The emt straps which hold bronze bushings to the table/gantry leave a lot to be desired. Large amounts of compliance/flex can be traced to them.

With my new build I hope to create either a 24x48 or a 48x48 system. Being a student engineer and for the sake of learning I hope to develop the router without using one of the available planned builds. More than likely the system will end up being similar to Joe’s 4x4 hybrid.

My major constraint here is money, much like everybody else. Though I can mill and turn down much of my own parts, which I hope will save me some money.

I already own Mach3, a unipolar 300 oz/in stepper setup, and a porter cable 7301 router which I intend to reuse. I am hoping to build all mechanical components for under $1,000.

I have much research to do though before finalizing my purchase decisions. I’ve separated the build into three major build components, Frame, Linear Guides, Linear Motion.

Frame: 8020 Aluminum Extrusions or Square Steel? Steel is cheap, though time consuming, and possible warping due to welding. I’m definitely leaning towards 8020 extrusions since they will accommodate for design changes later on.
Questions: Anybody find Steel/MDF/HPDE frames to be better given their price?

Linear Guides: I’ve seen lots of skate bearings riding on ¼ flat plate. Joe’s 4x4 uses roller v bearing riding on angle iron. Other systems use odd skate bearing assortments riding on gas pipe. I have not seen many or any of the larger systems using chrome plated round rails with bushings/bearings?
Questions: best bang for the buck? I don’t want to be disappointed later on with a non rigid build, from what I’ve looked at so far I really like the v groove bearings, but I haven’t worked out dollar amounts for each system yet.

Linear Motion: Rack and Pinion or leadscrew? Rack and pinion is my top choice, but cncrouterparts.com claims only 0.005” resolution, or 0.0005” with 1/10 microstepping. Microstepping does not improve resolution though (or at least by much).
Questions: Is it cheaper to go with acme screws/backlash nuts or cheaper to go with R&P?

Input is greatly desired, I have little/no experience in most of these areas, and I hopes to learn!

I have an excel spreadsheet which after I get more information I’ll be glad to share with others. I’ll update the thread with information as I gather it.

[DonFrambach]

One comment about linear motion. I just made a small 14x14 router using 1/2 x 10 single start ACME leadscrews. It seems to work fine, however, if I build anything larger, I'm almost certainly going with either 5 start lead screws or a rack and pinion drive because there is considerable friction between the leadscrews and the delrin nuts I used which severely slow down the speed.

[DonFrambach]

Another comment this time about resolution. The addressable resolution in a machine is often much finer than the actual resolution due to flex, backlash, etc. While it's great in theory to have high addressable resolution, at the end of the day, all you really care about is repeatability and accuracy.

[RomanLini]

This is a really nice fixed gantry design, easily made from welded steel tubing. It's close to 48"x48" or could easily be adapted to that size. The photo shows all the bearings and screw setups pretty well;



DonFrambach- You said about your Delrin leadnuts, have you considered the Igus plastic leadnuts? Their catalog shows much higher speed performance and improved life over Delin nuts.

[DonFrambach]

Originally Posted by RomanLini DonFrambach- You said about your Delrin leadnuts, have you considered the Igus plastic leadnuts? Their catalog shows much higher speed performance and improved life over Delin nuts.

Thanks, I'll look into it.

Don

[JohnnyVegas]

For ease of design and build my money would be on v groove bearings and rack and pinion.

I'm in a similar boat and working through various designs myself. I have screws and a ton of hardware so I'm more or less designing around the materials I have. By the time you factor in this screw and that screw, then gear them (I would/will) thrust bearings, collars, couplers, anti back lash nuts. Etc... You can get a Rack and pinion setup and still gear if needed.

That being said... I never had an R&P setup so I can't really say how great they are or are not but for cost/design time and overall ease I think I would go R&P.

Just my thoughts.

[tkubic]

I've been trying to price everything out and do more research. I've found that vxb and irvineman sell a v groove beawring for $15.00 a piece, angle iron is about $1.23 per foot from speedymetals, which puts me just over $200 for that setup. I'm not entirely sure of the accuracy I'll get from angle iron, and the quality of the bearings.

Using skate bearings I estimated about $150 using a setup similar to the cncrouterparts carriage with 6 skate bearings. This route requires me to mill all my carriage mounts, which shouldn't be much of a problem.

Being spooked about the quality of the vxb v-groove bearings, and pricision of cheap angle iron I'm leaning towards the skate bearing setup ($50 cheaper to).

R&P is looking to be fairly cheap to. I estimate roughly $400 (after shipping) using cncrouterparts R&P solution (which is marginally more expensive then me crafting my own parts).

As a side note: 1/4" x 4" aluminum plate is cheaper than 1018 and a36 steel?!!! sourced from speedymetals

[JohnnyVegas]

Originally Posted by tkubic I've been trying to price everything out and do more research. I've found that vxb and irvineman sell a v groove beawring for $15.00 a piece, angle iron is about $1.23 per foot from speedymetals, which puts me just over $200 for that setup. I'm not entirely sure of the accuracy I'll get from angle iron, and the quality of the bearings. Using skate bearings I estimated about $150 using a setup similar to the cncrouterparts carriage with 6 skate bearings. This route requires me to mill all my carriage mounts, which shouldn't be much of a problem. Being spooked about the quality of the vxb v-groove bearings, and pricision of cheap angle iron I'm leaning towards the skate bearing setup ($50 cheaper to). R&P is looking to be fairly cheap to. I estimate roughly $400 (after shipping) using cncrouterparts R&P solution (which is marginally more expensive then me crafting my own parts). As a side note: 1/4" x 4" aluminum plate is cheaper than 1018 and a36 steel?!!! sourced from speedymetals

I have a family member who travels on business to Asia as a buyer for Ping golf.

He's there now and is going to try and source some V-Grooves and bring them back for me. It looks like I need to purchase about 500 so I may have a few extra (lol). PM me in a few weeks if you need some v-groove bearings Abec-7 quality. Just cover the shipping and you can have as many as you want at cost. I will need to sell about 475 at this point.

BTW: I am convienced VXB stands for Very eXpensive Bearings.

[tkubic]

I've made a few decisions, and have come up with a first draft.

• 4'x4'x1' usable work area
• 1/4" steel or aluminum rails for strength
• r&p for x and y
• 1/2-10 single start for z
• all 1530 extrusions

Any feedback is greatly appreciated.

[jsheerin]

I'd add some 1530 rails to the bed to support the material being machined and tie the x axis rails together. I'd also beef up your gantry uprights and the attachment points of your bearings on the x axis (distribute the forces across the entire bearing block, not just to the middle), but I am fond of overkill. Do you just have 1/4" steel for the z axis? If so, add 1530 for backing (at least) especially with your long z axis.

[tkubic]

ya, i need to beef up the x-axis attachment points. I also need to provide support to the table to prevent wood creep. I'm thinking of adding square tubing to the z-axis to strengthen it in the +-x direction. I'm hoping to go underkill with easy access to strengthen after being built. For now I hope to keep the price as low as possible so that I can afford to get it done.

Thank you for your input. You reminded me of many things I have forgotten about. I need to make a list of these things.

[Phife]

That thing looks like its going to flex like no other!, definatly beef up the X toY supports, and I'd consider reducing the Z height, 12" is alot and will flex alot, why do you need so much Z travel?