I've been lurking for quite awhile and decided I need to have a cnc router. I'd be doing thin plywood, wood signs and general goofing off. Thinking of going with the Hobbycnc stepper/driver board combo and cutting with a Dremel or RotoZip. I'll probably go with the free plans (may make it a bit smaller) and fab it from MDF.
My question is this, will using 1/4-20 allthread be painfully slow. I was thinking of maybe 1/2-10 acme but read somewhere you shouldn't have the screw too much bigger that the stepper shaft.
Also I've got minimal tools for this (I'm an animator and tend to be dangerous around power tools :D ) Drill press, cordless drills and table saw.
Any suggestions?

Thanks
Dave

I am no expert..but I use threaded rod from hardware store with 2 sizes.
I am on a budget (wife says so) so most of the cnc is parts from here and there.
largest rod is for X....Y,Z are a step down from that one.
My X is larger than stepper shaft...no trouble so far.
Yes mine is slower than a cnc with a "real lead screw" but for now it does the job.
Also the X has a heavy router attached so the wear and tear is a concern on threads.
Balancing your weight is an idea...I had a cable and pulley working on a cnc that
you could lift the Z up and down with a finger tip like it was floating.

Good luck!

You can get 1/4" and 3/8" acme too. 3/8"-8 or 3/8-10 would give you much better speed than 1/4-20. Check out http://www.mscdirect.com , page 3856

GER21,
I have a question myself..I went to http://www1.mscdirect.com
Thank you for sharing that link with us, I never saw it before and its great!

Anyway my question is on right hand threads and number of starts.

First question
Is a right hand thread a standard thread type?
like what I might already be using from of the shelf hardware store?

Second question
What does number of starts mean?

I have learned so much on cnczone, what a terrific web site.

Right hand thread is standard direction.
A screw with more than 1 start has more than 1 thread wrapping around, alternating. A 1/2-8 2 start screw has 8 threads per inch, but only takes 4 turns to move 1 inch. Multiple start acme screws, 1/2" and smaller, tend to be much more efficient than single start threads, with some approaching 75% efficiency (3/8-8 4 start, and 1/2-10 5 start), vs 40% efficiency for 1/2-10 1 start acme. The tradeoff is that you'll need a little more power, because you lose some of the mechanical advantage of all the threads, but you transfer twice as much power. And, you get a speed increase by a factor of 4 or more, while keeping the stepper motor spinning at lower rpm's where it has the most power.
If you have big enough motors, the 1/2-10 5 start will give you awesome speed with pretty good efficiency. There is a thread here by InventIT whose router could rapid at around 350ipm with 400 oz steppers, and its a big and heavy steel machine.

The 1/2-8 2 start is only $23 for 6ft. from MSC, much less than the other multiple start screws they have. It's very good quality, too.

GER21,
IFirst question
Is a right hand thread a standard thread type?.

Yes.



Second question
What does number of starts mean?.


If you look at a threaded rod from the side where you'll put the nut on you'll see an entry to the thread. Normally you'll see one entry or one start. It's easier to make and almost all of the screws you’ll buy at the hardware store are like that.

Now lets take a ½” shaft and make a thread of one inch per turn. You’ll have very little "groove" and a lot of “not groove”. To remedy it you can put an other thread at 180° offset and with the same pitch an now you’ll have more "grove" per inch and a two start screw. If you’ll make the offset 120° you’ll have a three start screw. An offset of 90° will be a four start screw.

If I’m wrong of what I’ve said then just ignore it. :-)

Sheesh... took me that long to type that somebody else beat me to it.:-)

Sheesh... took me that long to type that somebody else beat me to it.:-)

I thought you were just adding to my reply. :)

There is a thread here by InventIT whose router could rapid at around 350ipm with 400 oz steppers, and its a big and heavy steel machine.

Holy cow, Batman. That’s like 6” per second. What can you cut at that speed? Butter? :-)

Yoram

Some commercial routers can cut through 3/4" plywood at over 1500 ipm. We cut 3/4" plywood and partical board at 400 ipm on ours.

Notice I said rapid in my post above. You need a really big spindle (at least 5HP, maybe more) to be able to cut that fast

I have to say thanks to all of you...Ursine started a topic and here I am getting help also. This cnc is still rather new like learing Gcode and all the G tricks.

GER21 mentioned going to MSC and boy once I got there I was like a kid.
Being on a budget it is nice to find options (my favorite word).
I wait all day for a cut with this hardware store threaded rod but after seeing
the prices like $23 for 6ft of 1/2-8 2 start acme lead screw I am now excited again.

I have a small question to add to this.
I want to mill aluminum for small parts, nothing real heavy hust some 1/4 to 3/8 inch
milling. I have a Bosch router with variable speed mounted on my router now.
QUESTIONS
Is this possible with what I have?
And if so what type of end mill do you suggest or where should
I go to puchase an end mill bit.

I understand about the up-spiral and down-spiral bits but not sure about type.
Thanks a ton gang!

Go to http://www.onsrud.com They have an entire catalog of bits specifically for aluminum. Bring your wallet. Or you could try some cheap endmills from MSC. Look for the high helix type.

Whether or not your machine can cut aluminum depends on a lot of factors, mainly how stiff and strong it it.

One more place to find Acme threaded rod is www.use-enco.com. I have gotten some threaded rod and some aluminum bar from them and have had great service and fast shipping everytime. Also if you order is over $50 and use promo code FCNUFS in the checkout you will get free shipping. My last order had 3 72" pieces of 3/4-6 acme threaded rod and some other stuff and shipping was free. The box with the threaded rod was well over 20 pounds. They sent me the promo code awhile ago in an email so i dont know how long its good for but it worked last week


Darren

Thanks Guys,

I'll probably start with the 1/4-20 just to get started...no sense spending more at this early stage. Plan on a trip to Home Depot this weekend.

Thanks,

Dave

GER21,
I went to www1.mscdirect.com signed up and ordered a lead screw.

Acme Roll Threaded Bars Thread Size: 1/2-8 Rotation:
Right Hand Length: 6 Material: Low Carbon Steel - C1018
Total $22.05

Sure beats trying to compete on Ebay.
I have tried that and always got outbid.

Your info has been most helpful!
Thanks again very much!

I have had fair luck with 5/16 18TPI threaded rod myself.
The rod is a bit stiffer due to increased diameter than 1/4" rod. I turned one end down to 1/4" using light pressure and a bench grinder. Turn until about 1/2 linear inch from the end is bare of threads, fits the 1/4" u-joint rod couplers I have mounted on my motors, direct drive.

A couple of pointers from what I have done so far:
1) Get rod as straight as you can find first. Some of the rods I have found at HomeDepot or Lowes were very dog legged.
2) run the rod trough a good quality Die to make sure the threads are straight. They get banged up in the bins and can bind if the threads are spoiled. I chucked mine in the drill, lubed with some oil, and made a few passes with the die to even things out.
Be careful, all of the rods I have turned this way make a lot of chaff!! some runners are suprisingly stiff, and they can poke ya in the finger if you arent watching.

They work fine for now, using 5/16 X 18 T-Nuts and wood blocks mounted on the moving axis.
Cheap, simple, and not a bad tradoff if you are on a bidget.

As of now, my motors turn about 200 RPM which gives me about 11iPM rapids. This is OK for me as I am using a Dremel for a spindle, and don't want to overload it.