[Thazul]

Hi all, first time poster long time reader.
I love all your work and can't wait to start on my own project

I have a few questions before I start buying a few select items, but first let me tell you what I am going to build.
Depending on what I can scrounge up I hope to do a machine with a workable area of 8' x 4' x 8 to 10"

I plan to have all my axis resting on LM type guides, and driven by ballscrews.

I have not settled on what type of motors to get, still shopping around. its hard ro find Servos+Encoders with Price tags Online, with the kind of torque I was hoping to use. So I was leaning twards HomeshopCNC's NEMA 34 sized steppers.

I just ordered my porter cable 7518, and am trying to get some rails right now.. once I get my rails I am going to get my steel and start welding my table. I will upload pics when I start construction


Ok on with the questions,

Is it a good idea to get the same ratio with all of my ballscrews?
If that is the case, most likely have to get them new from a reseller, any suggestions where I can get them from a reseller in the length I need for my X? around 105". I'm waiting on a quote from Lintech as we speak.

I was planning to use 2 ballscrews on the X, one on each side of the machine, each ballscrew individually powered by its own motor. How do I sync the motors to a single axis, can this be done with a single driver board?
Timing Belts with a centrally located motor is another option I am considering.

My machine will look similar to this great looking machine: http://www.inshorepowerboats.com/cnc.../CNCROUTER.htm
Except I am going to make my steel frame alot more stout.

Thats it for now, I'm sure I'll have alot more questions as time progresses.

Can't wait to get a project log going on here!

Thanks in advance!

Drew

[ger21]

Is it a good idea to get the same ratio with all of my ballscrews?

You don't have to, but I would for the X and Y at least. Ideally you want your X and Y axis to move at the same speed. If one is faster than the other, you won't be able to use the extra speed most of the time anyway, so I'd try to set them up the same. You might want to check out http://www.nookind.com

I was planning to use 2 ballscrews on the X, one on each side of the machine, each ballscrew individually powered by its own motor. How do I sync the motors to a single axis, can this be done with a single driver board?
Timing Belts with a centrally located motor is another option I am considering.
Drew

You need a driver for each motor. You can slave these together in software (Mach2/3), or both can be driven from a single step and direction pin from the parallel port. Your other option will work as well, but will need a bigger motor to get the same results.

[Thazul]

Thanks for the reply Ger

I think I am going to go with the Single Motor + Timing Belt.

Have any of you guys ever purchased Ballscrews/Ballnuts from McMaster.com?
When you order a special sized Ballscrew and lets say you specify 105" length, does that mean the thread length, or the whole length?
And where is the ratio of the screws listed? Maybe I dont know how to read it right
Are those ballnuts Preloaded / Zero Backlash?
Also why are the end mounting blocks so expencive? Can I have someone here make them for cheaper?

Thanks guys

Drew

[ger21]

The ballscrews will come threaded the entire length. You'll mave to machine the ends yourself.

By ratio, I think you mean the lead, which is how much the nut will move with 1 turn of the screw.

They don't appear to be preloaded, from what I saw.

I think those end blocks use expensive angular contact bearings, but the price is still pretty hard to justify. You might want to look at these http://www.misumiusa.com/Catalog.asp...-1,59914,59924
They seem to be much cheaper, but I don't think they will handle the same thrust loads as the expensive ones. Here is a little info on making your own. http://www.5bears.com/cnc04.htm

[Thazul]

Ahhh, Okay so I was reading it wrong.
When I saw lead I was thinking that was the size the ends were pre-machined to.
Ok so when reading Inch Ballscrews, if it says DIA 1.00 LEAD 0.20, thats 1 inch diameter screw, with 5 turns per Inch?
I was thinking of something alittle quicker.. would .5 lead be good for a machine my size?

Alittle bit of a setback. I lost the bidding on the linear rails I wanted.
Guess I'm not a good enough Ebay player to win auctions. I lost both of them.
Someone came along and (chair) 'd me in the last 5 seconds. And was unable to bid higher fast enough before it ended. :frown:

Oh well, More time to plan :cheers:

Back to the topic at hand, Ballscrews... Anyone know anyone that will be able to machine the ends of 8'+ long ballscrews for me?
Or can I buy them pre-machined?
I live in Phoenix.

Thanks,

Drew

[CRFultz]

Drew,
After losing many auctions to last second bids, I bought a book about Ebay and read about some of the tricks to winning bids. Here are some tips that might help in the future.
1. Make sure your computer time is the same as ebays. There is a place on ebay where you can check there time with yours. It needs to be the same.

2. Check your "time to post". How long on average does it take to post a bid?
You can time this by bidding low on high dollar items. use a stopwatch to check how long it takes from clicking the "place bid" box till the screen changes and tells you your bid results. this amount of time will change with traffic but if you do it enough you will get a average time. my average is 3 seconds.

3. When the end of the auction is close (less then 5 mins is good) open the main page and go thru the bidding process with the highest bid you are willing to spend. Do not send the bid. Min. the window and open another from the main page and start clicking refresh. watch the bid after each refresh. open your computer clock so you can watch the second hand.
keep clicking refresh.

4.while watching your computer clock second hand, when you get to your "time to post" click on your "place bid" box if you have been outbidded.

Keep in mind this will not always work because the other bidders are doing the same thing, but everyonce in a while your bid will get placed at the very last second and you will win only because time ran out.
This is called snipping.
Only bid what you are willing to pay for that item and nothing higher. Alot of people overpay because they get caught up in a bidding war the last few seconds and then regret it later. If you watch auctions you will get a ideal on what simular items are going for. I won 3 auctions for thk ssr20's and rails by doing this and i paid a very low price for them, the seller was not happy.
Good luck
Chuck

[ger21]

Forget 1-4. http://www.auctionsniper.com or any of the similar ones. Only way to go.

On a big machine, .5 lead is the way to go. Or rack and pinion. Our commercial router use 1" lead screws. The only downside is you'll need bigger motors with higher lead screws, but it's a lot easier to go fast. But rack and pinion might be cheaper, as you'll need some large screws for an 8ft axis.

[CRFultz]

Man, I went throug all that trouble and could of had gotton it done for me. Oh well...i won the bids and that was the objective..I like the ideal that i probably beat there computer to the punch. Must have been lucky that day.
Will keep that in mind for later bids though. Not crazy about paying for it but if i get what I want i guess its worth it.
Good luck anyway
Chuck

[ger21]

It's only a quarter an auction and you get a few for free, and you only have to pay if you win. I've used it 3-5 times, and haven't had to pay yet. The thing is, though, is that you have to decide up front what you're willing to pay, although you can go back and raise it if you want. Another nice thing is that if you change your mind, you can back out because the bid will not have been placed yet.

[Thazul]

Interesting Info on the auctions there guys.. I wonder why Ebay does not use dynamic bidding, its sort of unfair to both the seller and the buyers.

The rails I lost my bidding war on was a pair of SR35W2SSCO+2670L
I am not sure what happend but now im getting asked if Im still interested.
What do you guys think?
I was going to just ask the person to relist them.
I am kind of releaved I didn't win with how high my losing bid was.
Do you guys think they are worth over $1000 USD?
I'd like to be frugal about getting my machines parts, but how frugal can you be when trying to get such large parts?

Maybe you guys can tell me how offen parts this long come around?

Thanks for the input,

Drew

[2muchstuff]

Hang in there Thazul your auction will come. I too am building a large machine and in need of some long rails. About 8-12 weeks ago the ball bearing slide market was such that you couldn't give then away. Since then the prices that I have seen the go for is obsene. I was watching a few sets of rails like you were and they went ballistic, over $1000.00. I plan on working on another part of the machine until the price comes down.

[Thazul]

Thanks for the tip 2muchstuff, I didn't know the market fluctuated so much.
I have not been shopping in the market for very long, only about a week.
I guess it all boils down to having some patience.
I would like to do some other work on my machine, like buy some steel and begin to weld my main structure together.
But, I was kind of waiting to see what I could get in the market of rails before I was dead set on my table design/size.

I got a question, If I pick up some rails, lets say for instance 76" rails. and I want to use 56" of that for the Y axis. I could cut them down, and use the left overs for my Z axis? just have to buy some bearings to go on them right?

-

Drew

P.S. More people should use the chat :P

[2muchstuff]

You and I think too much alike. I was planning on doing the same thing for my Y and Z rails, buy them long and cut them up and find an extra set of trucks. The last set of 56" rails went for way too much. I can see the 80" plus rails going for a lot of money but the 56" ones. Well maybe not all of us think big. Someone who would only want a 48" x-axis would need a 56" rail.

[ger21]

35mm is a lot bigger rail than you need. 25mm is plenty big enough, and usually a lot cheaper. Our machine at work has a cantilevereg gantry that weighs well over 1000 lbs, and it uses 25mm rails.

[Thazul]

What do you guys think about buying Servo Motors Second hand?

Im considering a couple right now, and they are said to be in "Good working condition, with some cosmetic blemishes.

These are AC Servo motors with Incremintal Style Encoder. with a resolution of 32768.

-

Drew

[ViperTX]

What ya driving the AC servos with?

[Thazul]

Well nothing yet, I would have to get something.

These motors are a very good price, a better price than I can get steppers with the same torque.

they are 230volts and 11 continous amps.. this is more than the gecko can provide Amp wise, what driver board would I have to use?

-
Drew

I am in chat right now if ya have a second.

[austin.mn]

i must be lucky, i live in a small town and the recycling center gets a few old packaging machines about every year. the manager doesn't mind if i go through there and rummage through there stuff as long as i am willing to reimberse them for the stuff i take. (scrap metal price) so i get a lot of bishop wisecarver bearings and other misc components sensors and what nots for just a few bucks. you might want to have a look at your local recycling center, or even if there is one in your state. it may be worth the extra effort to pack up some tools and a lunch and spend the day there. it is more fun than disneyland if you stumble accross anything good. i see a lot of other people there looking for lawnmower parts and crap like that, most other people around just aren't into the stuff we like. last year a control panel came in with a full allen bradley plc, panelview, and a vfd. so you can get pretty lucky. they also get cars and other things in, so you can really get outfitted full of supplys to build your machines.

so far i have been able to build my own cnc router, an automated pocket whole drilling machine and several other small projects using mostly other peoples junk.

[ger21]

they are 230volts and 11 continous amps.. this is more than the gecko can provide Amp wise, what driver board would I have to use?

Gecko's and Rutex, the most comonly used "hobby" servo drives, are for DC servos, not AC. You'd probably pay more money for drives for those than buying new servos and Geckos both.

If you have your heart set on using servos, plan on spending ~$1000, minimum for motors and drives. Even using Ebay.

[Thazul]

Hey guys, what do you think about these servos+encoders for the X/Y.

-
Reliance Electric DC Servo motor
NEMA 34 Frame
Model 0690
Back EMF Constant, ke = 62 V/kRPM
Torque Constant, kt = 5.5 lb-In/Amp
At just 10 amps, that's 55 Lb-In = 880 Oz-In.
Nominal Speed Rating: 1750 RPM
Nominal Voltage Rating: 120 Volts
Continuous Current Rating: 4 Amps
Peak Current: 20 Amps
Continuous Power Rating: 1/2 H.P.
Motor Body Diameter: 3.38"
Motor Body Length: 9.0"
Shaft Diameter: 0.375" x 1.13" Long
Integral Encoder: Agilent P/N HEDS 5605#A06
500 Line yielding 2000 Counts/Rev.
Encoder is mounted under protective steel cover on tail end of motor.

Also says:
*** THESE WORK WELL WITH GECKO DRIVES.
The lower voltage rating of the Gecko is not a problem:
With an 80 volt supply, you can expect
~1200 RPM No Load Speed
~1100 Oz-In Torque

-----------

1200 RPM's, does that sound kind of low for a servo?
I think I can get these for around $230-$240 piece, is that decent?

Thanks,

Drew