1/4-20 lead screw=Painfully Slow?

[Ursine]

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 ) Drill press, cordless drills and table saw.
Any suggestions?

Thanks
Dave

[solarchimesam]

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!

[ger21]

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

[solarchimesam]

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.

[ger21]

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.

[ger21]

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.

[TigerPilot]

Originally Posted by solarchimesam 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.:-)

[ger21]

Originally Posted by TigerPilot Sheesh... took me that long to type that somebody else beat me to it.:-)

I thought you were just adding to my reply.

[TigerPilot]

Originally Posted by ger21 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

[ger21]

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

[solarchimesam]

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!

[ger21]

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.