[madtownrob]

Here is a long winded post and looking for some input:


I have been looking at going to a R&P setup and re-building my Joe's Hybrid 4x4 with a steel base on the machine. Being cold in Wisconsin and having limited time in the shop, I haven't wanted to turn on the heater out there and try to warm it up to sit down and come up with some ideas for what I want to do. I want to change from lead-screws to R&P because when it is below 55 degrees in my shop, the AB-nuts get tight and I loose steps. Over the last few week I finally put on paper my brainstorming on what I think I may do, and I am looking for some input on placement of the rails on the X gantry and sizes of rails to use. Here is my thought process in no particular order:

My upgrade will be most likely the following:

Linear slides on all axis, 15,20, or 25 series with 2 bearing blocks per axis - but may go with only 1 per slide on the X gantry if I go with the large 25 series rails.

Use one of the linear actuators that I have for a new Z -most likely one of the 2 KR33 with stepper mount and ball screw. I also have a linear stage that is really nice, however I need to build a mount and get a screw and AB-nut for it so I will be most likely selling it.

I will be using 1/2" aluminum side plates for the Y carriages, and R&P on X and Y from CNCrouterparts.

A new 8020 X gantry beam - a 15-3060 3"x6" fractional to replace the metric 25-5010 that the Joe's uses right now.

It looks like the 15mm series linear slides/rails may be a good choice mathematically. Each bearing block can support 80 lb-ft of moment force on them so 2 bearing blocks per rail gives 160 lb-ft of carrying capacity per side for the Y. If I step up to the 20mm series it could support a moment of 165 lb-ft per block - so 330 lb-ft per side on the Y. I am unsure if I really need the capacity of the 20 series rails The 15's on the X gantry can support a 98 lb-ft moment per block - so with 4 to support the Z almost 400 lb-ft- I see no problem with these on the X with 4 blocks holding the linear actuator of the Z.

The 15mm works out rally nice for the Y on the 8020 because they are 24mm thick from the face of the 8020 to the mounting point. A 15mm rail and block mounted to a 1/2" aluminum side (13mm) = 38mm - This is good because that means if I mount the rack on the 8020 and use a CNC router parts R&P drive that I will get nearly full engagement of the pinion on the rack.


Now looking at the 20mm rails - it would push the R&P out an additional 6mm to 42mm total. A 3/16" aluminum spacer would be needed be be added to the back of the rack to bring it back out to match the location of the Pinion.

Then throw in the 25 series - may be overkill - but I would then need bring the rack farther out from the Y axis 25-5010 extrusions - most likely mount on top of the 25-5010 to avoid that.


I have a few pictures of what I am thinking of for the X. Either mount one slide vertical and the second slide on top of the 8020 to support the R&P drive, or both on the horizontal face - these are labeled 3&4 in the picture. I am leaning towards #4 to support the horizontal member that attaches the R&P drive. This is similar to Greolts build.


I have some more sketches of the 15 series and 20 series for the Y axis gantry side plates. the 20 series will require some additional machining to make sure that I can clear the blocks with the R&P drives. I am not sure if I can get this to work out. The 25 series end out working Ok with the 2-hole blocks mounted on the side of the 25-5010 and the 4-hole blocks would need to be mounted on top or bottom of the 8020 to allow engagement with the rack on the side of the 8020.

My issues:

- the 15 series appear to be just too darn small. They connect with small fasteners - 4mm for rail to 8020 and 5mm to the blocks. I haven't done the math on the shear forces yet but I am sure that it is close to exceeding the connections. Look at the pictured of the comparison of 15 to the 25 series!

The 20 series are used on some other commercial machines and use 5mm fasteners for rail to 8020 and the rails, and they just appear to be beefier. But these cost!

The 25 series may be overkill but they use 6mm fasteners to connect the rail to the 8020. This has a 7mm hole and fits a 1/4" fastener fine.

4mm and 5mm t-nut hardware from 8020 is EXPENSIVE. I need 128 to attach the rail and many of them are $2.00 each

so an additional $250 for the hardware to attach the smaller rails. I could get 1/4" nuts for $50 for all 4 rails

if I use the 25 series and use the $200 towards the bigger rails.... trade offs everywhere...

Load capacity of blocks and rails I am looking at:

15 series 80-lbft per block - 4 hole
20 series 165-lbft - per block - 4 hole
25 series 268-lbft - per block- 4 hole
25 series 56.3-lbft - per block 2 - aka - it's a smaller block

So the big question is, what combination? I know that the 15 work on the X, and Y but are too small IMHO, the 20 series work - but fasteners get expensive, the 25 series are expensive but the fastener costs are reasonable. The 25 2-hole blocks have a substantially less load rating than even the 15 series. But on the Y sides - this gives me 112lb-ft per side. My gantry weights 50 lbs (about 1-ft high)- so the questions is - will I generate an additional 50-ftlbs of cutting forces? The documentation that I have been reading say that the 2-holes blocks on a wood machine should be adequate - we will see what everyone else thinks

My break down: (don't choke on the costs)

Y&A listed first, then the X, cost is with shipping and fasteners

#1 25-2hole and 15 cost = $865 - cons: the 15 are awfully small!

#2 20 and 15 cost = $890 - cons: fasteners and again the 15 are still small

#3 20 and 20 cost = $1,025 - cons: one of the most expensive options

#4 20 and 25-2-hole= $930 - cons: may look weird since their is a larger 25 on the gantry

#5 25-2hole and 25-2hole cost = $905 - cons: smaller load capacity of the 2-hole block

#6 25-4hole and 25-4hole cost=$995

#7 25-2hole 25-4hole long sides (1 per rail on X) cost = $905 - this option has a longer single block on X axis rail to support the Z slide

#8 25-4hole 25- 4hole long sides (1 per rail on X) cost = $948

I am leaning to #5,#7 and #8. I just need some reassurance on the 15 series - again they are so small in comparison to the 25's! (picture!)

Thanks for any input that anyone could provide! I am having a heck of a time with this forum allowing me to upload photos - see these are just linked:

[Drools]

I have been doing some home work on the THK product line and from what I can gather the SR and SSR line of LM products are best suited for horizontal loads.
It looks like you have either the SR or SSR type. I'm no expert but the rails for the SR and SSR bearing blocks look to be the same.
Have you thought about the best mounting and placement for your THK SR/SSR products?

SSR.
The compact design with a low sectional height and the ball contact structure at 90° in the radial direction make this model an optimal model for horizontal guide units

SR
Since it is a compactly designed model that has a low sectional height and a ball contact structure capable of receiving a large load in the radial direction, this LM Guide is optimal for horizontal guide units.

[madtownrob]

Drools - thanks for replying...

I am looking at hiwin LG series (gothic arch - single row) or THK HSR/SHS series 4-way/45- degree series. I have researched what you are saying about the loading on the 90-degree single SSR or SR series and am turned off by that. Here is a good comparison of many different rail/block MFG's - I noticed that between the Hiwin and THK's - hiwin can allow 25%+ more load in all directions...

http://www.matara.com/media/usr/pdf/...r%20Guides.pdf

My issue is - does a wood router's guides really need to be able to handle 270lb-ft of moment force per block, or will 56lb-ft of moment force per block suffice? I know that any of the blocks will be able to handle the dynamic and static load in X,Y,and Z directions - but it is the applied moment that I am dealing with.

Love to see some of your design!

[Drools]

That is the same thinking as I went with, you can't go wrong with the universal mounting of the SHS/HSR blocks. I hear the HIWIN parts are quite a bit less expensive than the THK parts which is a plus for people first starting out. I have spent some time looking for deals on the THK parts and have managed to find some but not a complete set. My current router uses the carriages from cncrouterparts.com and I'm very happy with them.
My first router is small but I have been learning a lot and that is what I was after. I needed something to keep me thinking all the time and this stuff is quite in depth.

[LazyMan]

Any updates on your mods?

[madtownrob]

Any updates on your mods?

YES! thanks for reminding me! I ended up going with Hiwin 20 series heavy duty flanged rails and blocks. The blocks have a light pre-load and are actually a heavier of a pre-load from what I though from reading the lit on them. I was used to v-bearings on rails where I could literally give a slight push on one end and have the carriage roll to the other. That is not going to happen with the rails. It's not a problem - just mentioning it. With that preload comes great rigidity to the gantry.

The X and Z are attached with option#4 - one horizontal rail and one vertical rail. I attached the Y carriages as shown in the second picture on the right with the rack mounted to lower slot of the 8020 rail. I had to shim out the rail with some 1/4" x1" aluminum to get full engagement of the pinion on the rail.

The gantry with sides, x beam, Z, and all the other drive motion weighs almost 100 pounds. I am driving it with Keling 387's and a g540. I can run 750ipm with an accel of 75 on the X,Y& A and it is plenty fast for me. The Z mounted on the KR33 6mm lead ball screw is set at 200ipm with the accell slider maxed out in Mach 3.

will get some pics up later.

[madtownrob]

Here are some more pics from the upgrade of my gantry. I cut a hole through the right end plate to pass both the 8020 through as well as the linear rail that I really didn't want to cut. This will allow me 2 things: 1- if I ever need to go wider I can, and 2 - I can easily adjust the width of the gantry to match the exact width of the gantry rails without having to cut the linear rail or the 8020 beam. It made sense in my mind at least and it seems to work well!

[madtownrob]

some more pics:

[jessyjames]

Rob you build is looking very promising indeed. Once completed this is going to be an great addition to what you already have... I am trying to catch up to speed with your build and get the overall concept of what you are trying to accomplish.

Keep up the hard work and keep the pictures a coming..

James

[LazyMan]

Looks nice and solid with those beefy extrusions.

[madtownrob]

The difference between the 5010 gantry beam that I used to have (and still use the same extrusion for the Y and A side rails) and that new 15-3060 is night and day. There just doesn't appear to be any torsional deflection now, even with the long moment arm that the Z-axis put on it with the full 9" of cutting capacity and clearance under the gantry.

I need to finish/tidy up some of the wiring. I am going to try the DB9 cables out for a while to see how the work out.

Also, I was using some mechanical micro limit switches and I am thinking of going with magnetic/hall effect switches- anyone have a good link here on the 'Zone of some examples?

[Aryantes]

Check out this thread for the hall effect switches

http://cnczone.com/forums/showthread.php?t=101878

Build looks great. The 3060 looks awesome.

I started my build a few months ago and now, every time I see large blocks / extrusions of aluminum I get excited.

[madtownrob]

Aryantes - thanks for the quick link. I just subscribed to that thread and will read through it this weekend. Hoping to use with my G540...we will see how that goes!