[pete from TN]

Definitely go with the larger hose barbs to make it easier to run the encoder lines thru. You can take a light gauge rope and suck it thru the tubing with a vacuum or blow it thru the tubing with compressed air and then use it to draw the wires thru carefully. I have all of my encoder lines running in surgical tubing and it is pretty much sealed up. If you decide to go with o-rings one on the back would be fine but I made the bottom of my housings pretty thin to make sure the stud on the back of the motor stuck thru enough to engage the bushing properly. I used RTV silicone sealant on the back of the housing to seal the motor and on the front to seal the lid. It works great and is really easy to do and just wipe off when it is done. An o-ring groove in the lid would be cool but you would have to figure out just the right size or buy o-ring material in length and try to seal it together. Should be pretty cool but mine are setup so that the lip of the housing does not have enough meat with the lid holes and housing securing holes to allow for even a small oring... just seal it up however you wish and make sure it is airtight... peace

Pete

[rwskinner]

You convinced me, I think I will do the surgical tubing. Just seems like it's simple and effective. My housings are from 0.750 stock with a .500 pocket so I have .250 0n the bottom to play with. Plenty of room for the bushing, a little tight for the 1/4 NPT fitting although it will go.

I thought you had some leakage issues early on? Where did they leak?

[rwskinner]

Oh, housing two came off the machine about 30 minutes ago.... Maybe tomorrow I can finish up the other two, and get the 1/4" NPT in the bottoms and the o-Ring grooves in them. I may even crank out the covers if I have any aluminum left. Damn, that stuff evaporates around here!!!

[rwskinner]

Pete, on the back, I think I'm just going to put a .750 o-ring around the center .500 hole in the housing. I'm locktighting the screws so I don't think anything else is required.

On the front cover, I got looking and there isn't much room there for a groove unless it's real small. I keep tons of o-ring stock here so making one is no problem but this one would have to be pretty small diameter o-ring material. So, I think you convinced me on the black RTV there as well. Any dimensional changes on the front cover won't hurt squat.

[pete from TN]

I used at first some rubber material I had in the shop here to make gaskets from and it was not suitable I guess. Since then I have been using the RTV and I just took everything apart to check on an X axis noise issue and it was dry as a bone. The noise issue was from a wire I had going to the BReakout board from my 12 v pps that was not properly shielded. I replaced it with a shielded wire and now it is back to being quiet again. You should just do the o-rings if you want to it will work fine and be easy since you are making them new now. I do not think everyone should do what I do because that would be boring but I have done some things that are really working great and if I can help others here I will do it. It is important to be able to seal this stuff up good and I still have a few items to cover up on my mill but I am running flood now for awhile. I really like the flood coolant and once I get a larger pump it will really help out with the hoggin'... good luck ...peace

Pete

[pete from TN]

automotive RTV sealant which dries clear but is kinda blue when you open the tube.. peace

Pete

[rwskinner]

Dang Honeywell limit switches on my SX3 keep getting wet and then I find the covers broken. I barely snug those covers but the coolant is making the rubber seals swell and deform. I used two of the three I bought for the RF45 to replace on the SX3.

Hum, I may have to go a different route, they are suppose to be swamp proof. The one for my X is also covered by alum. angle iron off the back of the table and it still gets swamped.

I may do something like Bob Warfield did. I guess his are working out ok. I like his aluminum housings for the optical switches.

I hadn't had a problem just until recently then 2 fail this week!! Sux.

[pete from TN]

Those switches on Bob's machine are not Bob's design rather they are from IH and they are excellent switches. I have them on my machine as well. I bought two of them from Himykabibble and made one myself. They are sealed with an internal o-ring on the shaft on both sides and have a similar seal on the lid to what you are doing with the encoder housings. They are also pretty simple. If you do a search for IH limits I think you will find what you are looking for. They use a 1/4 inch shaft I think and I used drill rod for mine.... They make it nice because you can put them anywhere you need to and the shaft and some collar stops take care of the positioning... peace

Pete

[rwskinner]

I have to order some material so I can do the covers.

[rwskinner]

What is the setting on your encoders Pete?
If I did my calcs right, I can only set mine to 125 count at 35 khz but I'm not sure if I figured it right.

I will be using 5 turn/inch screws,
My servos are
KelingInc KL34-170-90
4200 @ 90 vdc Or 3733 no load RPM @ 70 vdc that I'll be running
Times 0.8 = 2986 Max RPM / 60 = 49.76 Revs per Second
35 khz / 49.76 = 703
703 / 4 (for Quad) = 175 encoder setting??

Does that sound right to you?

Mine has worked at 65 k before but I backed it down to 45k. It does allow slightly faster rapids but ya gotta play with the settings to get it to function right.
Pete

[rwskinner]

Let's see if I have it right now.

My plan is to run Mach at 65khz, it tested fine.
I will be running my encoder off the motor shaft, and I will be geared down 3:1 and be using 5 TPI screws.

Encoder Setting
My Max Motor Loaded RPM @ 70 vdc = 2986
2986/60 = 49.76 rev/sec
65Khz / 49.76 = 1306.2 / 4 = 326.4

So the next lowest setting on the AMT102 is 256.

Steps per inch
256 count x 4 quad x 3 gearing x 5 tpi = 15,360 steps per inch.

Max Rapids
2986 rpm / 3 gearing = 995.33 / 5 tpi = 199 IPM

[pete from TN]

I would figure for 45khz tho... I can run mine at 60k but I keep it at 45k to help preserve the computer a little ( dunno if that works or not) Mine are at I think 500 lines setting but not sure on that one. Just figure your highest line count setting to get the speed you want at 45k and you should be fine. It is a trivial matter to change the encoder count on the AMT's so I would just setup for maybe 500 or so and see how she runs. You can figure your actual resolution with these figures and it is beyond me but my pal Art has some kinda spreadsheet he got from Mariss Fremannis that breaks it all down. For my setup and the speeds I wish to achieve as well as the most USABLE resolution the 500 line setup seems okay. You can crank it up but then your computer has to keep up and send out those signals at the max freq. to move the motors at your chosen rapid speed. On things like this it seems it is better to target ranges that are not max performance rather somewhere just south of it to help things last longer... Peace

Pete

[pete from TN]

Those numbers look pretty good. Should put you in a nice usable range and still have good performance. It seems like everything in this stuff is a tradeoff sometimes doesn't it. I have a very similar setup to what you are using and it is fine for my needs. I get pretty decent accuracy and speed but for someone else it might not be enough. Ya also gotta take into account the overall accuracy potential of the machine itself. You can put world class parts on a chinese mill and it is still a chinese mill unfortunately. You cannot polish a turd as the saying goes. Having said that mine is looking pretty shiny right now!! peace

Pete

[rwskinner]

I can dick with it some later after I get it going. I have the little SX3 tuned down to 100 IPM and that is more than fast enough for me. I was calculating max, then I can detune from there. Just wanted to make sure the ole pumpkin was adding the numbers right.

[pete from TN]

Sounds like Pumpkin check positive,over..:stickpoke Peace

Pete

[rwskinner]

I need to make a choice on rolled ballscrews pretty quick. I'd like to go with 3/4" ballscrews all the way around but I need to really check if there will be room under the table for the ball nut.

Who's ball screw? I'm still looking around, I went with Thomason on the lathe and ABBA on the SX3.


Pulley combination I'm looking at, let me know if I'm running into any GOTCHA's.

3:1 Ratio all axis, 200XL with 3/8" wide belts
20 groove on Servo 1.275 OD" with 1/2" ID Hub
60 groove on Screw, 3.800" OD with 3/8" ID Hub

In the 60 groove, I was going to go with a 1/2 ID Hub, but the ballscrew has a root of 0.575" which doesn't seem to leave much for steps for the bearing, threads, then 1/2 shaft for mounting.

I was thinking the 3/8" id will get me plenty to work with and I would "like" to keep it off the shelf, but 3/8" doesn't seem like it leaves much there.

[mattmark]

I need to make a choice on rolled ballscrews pretty quick. I'd like to go with 3/4" ballscrews all the way around but I need to really check if there will be room under the table for the ball nut.

hey, not sure about your rf-45, but with my MWT (zay7045), it's a pretty tight fit, but doable for 20mm (0.8") from linearmotionbearings (RM2005). the ballnut flanges are virtually at the bottom of the x-axis mount.

[pete from TN]

I used the roton ballscrews on mine and they seem pretty good so far. I used the 3/4 inch ones on the Y and Z and a 5/8 inch one on the X axis. I machined my own double ballnut setup and made a relatively low profile mounting setup. It is still a relatively tight fit getting the table on and off when I need to. I have to remove the Gib strip and kinda slide it over so the dovetails can kinda slide inside each other a bit which allows the table to pivot slightly on the ends to get over the ballnut mount and more specifically my one shot oiler fittings mounted to the carriage and they are not the larger plastic ones rather some very low profile brass ones. I know people have fit 3/4 inch screws inside there on some but it has gotta be a real tight fit. Since I have the 3/4 on my Y and Z and the 5/8 on the X axis I notice NO difference in accuracy, power, or movement on the X axis as compared to the others. Remember that the screw is captured at both ends with the undriven end floating in a radial ball bearing with a slip fitment. If you look at the linear strength stats of these screws you will see pretty quickly that their rigidity along their length assuming proper support is MUCH MORE than these machines could ever impart to them. Going with the 3/4 inch screw is really not going to give you any more power, accuracy, or rigidity in the grand scheme of things in this application. When I built my machine I had never heard of linearmotionbearings and from what I hear they are decent quality screws. If I were to buy them from him I would probably go with a preloaded double nut setup with flanged nuts and use belleville washers to load the floating nut. It is a simple way to go and actually easier to machine your mounts. Just make sure you buy nuts with dimensions that can fit under your table. Just some thoughts here on ballscrews now that I have a proven setup... peace

Pete

[Maglin]

Richard,
I was looking at the LMB ballscrews and going with Roton is far more economical. It's about half the price. That is including 2 nuts per axis for zero backlash nut housings. I wouldn't go with 3/4" all the way around. I think you will have problems on I think it's the Y axis for room. I'm personally going 5/8" on X and Y and 3/4" on the Z. Since Roton sells by the foot for screws I'm going to get a lot of extra screw. I tend to measure 5x and cut 2x for some reason so I'm giving myself a lot of extra screw on each axis for error and when it's alls done I'll probably have enough screw left over for a small project. I don't think you have to worry to much about deflection on the X and Y. It's the Z that has a constant load on it being gravity and the weight of the head. Even with a counterbalance or gas strut you still have a lot of weight to move against gravity, so I definitely think 3/4" screws are warranted on the Z.

My plan is to go with Roton in the beginning to find out how much screw I need then down the road change over to the very hard RC62 Nook screws. Then I'll probably just sell my conversion on here to someone like myself that would love to have the parts machined and just be able to do a little machining on the machine to install a kit like conversion.

I'm not to sure about the LMB screws as far as quality goes over the Rotons. That and I don't want Metric screws on my machine personally. Those are my thoughts. I also wouldn't get the flanges for the Rotons as you would still have the same issues of them backing out since they just screw on and held with a set screw. I'm going to probably just going to use a flat and set screw in the mount and see about being able to pin it. Like turn a nice groove in the threads of the nut for a 1/4" roll pin to slide through. I've still not nailed down how I'm going to pin it but I want to pin it for sure.

Also I'm thinking 1/2" on the screws for the gears is adiquit. The motors have 1/2 shafts that are keyed. I'm going to cut keys in the screws so I can use the same hardware. If you want you could build a quick forge and heat treat harden the screws. I'm debating on doing that but I don't know what steel the screws are made from. Probably a quick Oil quench would be best and then stress relieve them. I'll let you know how mine goes. I also plan to stone the screws so that the balls have a very smooth even surface to ride on. I'm looking for the correct stone to purchase now. I'm probably going to make a stoning fixture so I can stone 2 threads at a time and apply even pressure with the stones.

Ok that is a lot of idea's.

[rwskinner]

Thanks for the input on the screws. Ballscrews are something you don't want to buy too many of due to screw ups

I've always gone direct coupling, so this is the first time using timing belts in a CNC application, or even servos for that matter.

My servos will be mounted pointed back towards the screws to save space. It looks like for the X & Z they will have 8" center spacing and a 10" spacing for the Y.

Is there any good rule of thumb on when I start requiring idlers to help tension the belts or is it fine as long as there is plenty of contact teeth. The calculator is show 9 of 20 teeth are engaged on the servo sprocket.

8 to 10" seems like a lot of distance that might add to additional slop/machanical backlash when changing directions.