Z axis...how far?

[cyberdine]

Hi folks, as you can tell I'm a newbie in the business.
I've been gothering info to build a cnc router.
I want to be able to work some 3D pieces out of aluminum, these pieces will probably be less than half inch high X 5" long.
How would I determine the distance the Z axis have to come down???
Lets say if the tool will be 4" distance from the table, if I have a Z axis that can travel 4" down would that be enough?
I don't know if I am explaining myself well.
I appreciate any help.
Thanks,

[andy_ck87028]

An interesting question.

The distance the z axis must travel primarily depends upon how deep you want to cut.

However, in the most part you might need to cut thin pieces and only have a need for cutting deep very rarely.

This creates a dilemma as the Z axis will be extended to its max for cutting thin pieces and when it is extended it is likely to be least rigid and therefore least accurate.

So, in effect, if you build for a 6" deep cut to be used once a year and for the other 364 days cut shallow then your machine is working inefficiently for most of the year.

I think the best way to solve that is to have a variable height table so that shallow cuts can then be done without the z axis extended. When the z axis is not extended the machine will likely be more rigid than when extended.

I hope this adds useful information for you to determine how to design your z axis.

Andy

[cyberdine]

Hi Andy, thanks for replying.

Your idea is in fact brilliant...that didn't cross mi mind and makes perfect sense.
What you say it would be appropriated then? I see that most routers have in average 2".75 to 3" on its Z. Would you say that this distance would still give the system firmness?
I will definitely work on a table that can travel up and down.
Thanks so much for your help.

Alex

[andy_ck87028]

Alex

My pleasure.

An alternative to having a variable height table is to have multiple fixed positions on the gantry.

That would work better for a cnc router with a moving table but the problem is that with multiple fixing heights on the gantry, each time the z axis assembly is moved, there is a risk of losing vertical alignment.

Horses for courses.

Andy

[LazyMan]

This may not be the most practical solution but you can build your machine with a bit more gantry clearance that will accomodate working with taller parts and then you can stack material to raise your part if you are cutting thinner material.

I suggest sitting down and really thinking about what you want to cut with the machine. If you are going to primarily cut thinner 2.5D parts then you could get away with 3 inch z travel. If you are building just a home machine to mess around with that doesn't have a specific function then I would strive for as much z travel as possible because you really dont know what you are going to do with it. On my machine I got a 6 inch Z travel because I wanted to be able to carve out some 3D parts as well. As you aready know, you have to be careful because a lot of Z travel calls for a rigid design.

[cyberdine]

Hi Lazymen,

Thanks for your post. Its great to hear from several professionals.
I am gathering the most information, I don't want to build the machine and them think...I should have done this differently.
I am working on a plan (looking for some as well).
Initially I'll be working up to 3" thick aluminum but its always nice to have the machine built to accommodate thicker materials.
Is there anything in special that I should be aware of building the machine to work with aluminum??? stronger Z motor etc...
I appreciate all of your help.
Thanks again,

Alex

Ps. I plan on building a machine about either; 24X24 or 12X24, aluminum frame.

[LazyMan]

Its great to hear from several professionals

heh, Id love to think so but, I can't really call myself a real professional. Perhaps the others are though

Is there anything in special that I should be aware of building the machine to work with aluminum

Im inferring that you are building a "home" machine so you probably aren't looking for blazing fast feedrates, although you probably dream about it.

What kind of tools do you have available to you? Mill, lathe, basic hand tools?

For a machine your size, I would definately consider using 80/20 Extrusions or some other brand. You can get them on a ebay surplus store for cheaper. Extrusions are easy to design and work with. I have seen wooden machines cut aluminum slowly but if you are serious about it you will want to build your machine as rigid as possible.

Heres a router built from 8020 extrusions and extruded aluminum plate that I personally found to be a real great job. He build this without a mill so you can see that you can build a respectible router without serious tools.
http://www.cnczone.com/forums/showth...highlight=8020

Heres my build log of my aluminum machine. My machine has been finished for a while but have been a bit lazy and havent updated my log. My machine is not exactly built like a tank but I am very impressed with its cutting.
http://www.cnczone.com/forums/showthread.php?t=50790

Tell us more about your buget, skills, and tools available so we can try to give some more specific advise.

[cyberdine]

Hi,

I have a good amount of hand tools, one of those 3 in 1 mill lathe, which I've just got it from a friend.
My budget, probably around $1500
I have a little bit of skill, not a pro.

I like your design, really. That looks solid enough to me.
Do you happen to have a set of plans for it? I'll buy it.
I really liked your machine.

[LazyMan]

Hi, I dont have a real organized set of plans but I have solidworks models and some drawings that arent dimensioned to standards. They along with other data are currently being recoverd from a failed hardrive so Ill let you know when I get a hold of them.

I must warn you though, it cost around $2700 to complete my machine. It could be built cheaper but I baught almost everything new because I really dont have the time and space to slowly collect items from ebay. Sometimes I waste money because of convinience too...

Dont let the price frighten you. Most of the money was spend on expensive electronics (gecko 203v drives, dual breakout boards, control pendent) and linear motion equipment. The raw materials cost $600 to build including those expensive bosch extrusions. It really isnt the greatest design and you really need a nice mill to build it, atleast if you want to build it nice and acurately.

There are many ways you could go about this. So what are you cutting the 3d aluminum parts for? Are they mechanical? for RC vehicals maybe?

I just want to know because if your primary interest is in smaller aluminum parts you may want to have a look at a sieg X2 mini mill conversion. I believe those can be done for under $1500 and are more suited for metal work than a router.

[cyberdine]

Hi, $2700 should be ok...I am not going to spend this all at once anyway, within 2 months that should be no problem.
Right now I want to make so badges for vehicles and cut some carbon fiber with it. I know that this is more than I need for this application.
The thing is that I want to have a nice rig should I need to use it for something else that would then need a better machine and then I'd be stuck with a lower grade one.
So I prefer to go the long and more expensive way to get it done better.

I'll pm you.

Thanks for all of your help, I really appreciate it.

Alex