Chain drive options

[sd79jturner]

I am converting a cable drive to a chain drive and could use any tips, advice, warnings, etc.

[bruce_clark]

Jim,

Here is my two cents: GO WITH THE RACK AND PINION!
There is a world of difference between the rack
and pinion and the cable drive. While it may cost
a little more, the improvements are so astounding
that I could not believe it.

My machine was originally a cable driver. I was
able to convert it to r&p in about 2 hours (and
most of that was taking off the old cable stuff).

One of the things that makes this conversion so
much better is the larger stepper motors. By only
going to a chain, you will not gain the same
improvements and thus you will be cheating yourself
in the long run. Oh, did I mention that
repeatability is MUCH better too?

Bruce Clark
bwclark@centurytel.net (mailto:bwclark@centurytel.net)

[birdsofplay]

What Bruce said !!! doubled !

however ...

When the notion of chain drive first was offerd I thought it was a good idea because it followed the main SB philosophy of lowcost but effective parts.

However, on further investigation I arrived at the conclusion that "direct chain drive" would NOT be of much use because the machine would loose cutting/moving/plowing power, because we cant obtain a small enough sprocket. To be sure it would be faster with a larger drive sprocket but only at the expense of lost cutting power.

Therefore I designed a gear reduction version to accomodate standard sized sprockets and gears.
At first I used cogged belt drive to run the 9 tooth sprocket for my .25 pitch chain.
When I found the belts slipping I resorted to straight gears and havent had a problem since.

I did this project because I like to "play" with the SB design which provides an excellent basis and foundation. Also I had these parts "pretty much" for free. You may want to consider your costs as well as your machining skills before launcing into this undertaking.

Pix of my efforts, such as they are, can be provided on request, OR they're somewhere here in a past forum discussion.

[matomey@home.com]

Options, Options, Options...

There are about as many ways to make these things work as there are people.

I do not own a shopbot (yet!), but I have built a few homemade CNC devices. I currently use a belt drive on the X axis of my mill (72 inches) with a 20:1 gearbox and a 450 oz stepper to move it. I get 50 ipm moves and can push/pull through ANYTHING! I'm still behind in software with DANCAM, but for the price, it does a great job.

The chain drive has worked for me on shorter distances, so does all-thread and a brass nut. I think the rack and pinion would be good for the longer distance of the axis involved and wouldn't be bothered by sawdust as all-thread or a well oiled chain.

I think the shopbot is an excellent tool and defintely worthy of praise. I'm moving "up" to it because of support, speed and flexibility, plus this forum.

Mark Tomey
Homebrew CNC