Is this gentry design too heavy?

[Swiss]

Hi all,

I'm sketching out some ideas for a solid granite based gantry mill for high speed machining with small milling cutters.

Estimating the weight of the moving gantry part of the machine, I'm looking at something between 70kg and 100kg! This sounds pretty heavy for something which could be travelling at 2m/min.

It's 18kg for the spindle, plus another 18kg counterbalance to remove vibration, plus 30kg for the granite slab. That's already nearly 70kg. Plus linear motors, rails, etc.

Is this a normal mass, or am I crazy?

Hugo

[Swiss]

Here's a screen shot, showing the X axis gantry mounted on the Y axis on the base.

[CarveOne]

Originally Posted by Swiss Here's a screen shot, showing the X axis gantry mounted on the Y axis on the base.

When you decide on what is the largest size board outline that you will want to route, add the gantry width at the rails, and add any extra travel that is needed for your clamping fixtures. You may find that the board outline will be doubled (or more) to arrive at a workable table area that you can live with. The width of the Z axis needs to be considered also. Also consider that adding limit switches will require additional travel distance as a "stopping zone". The object is to have the router bit make the largest outline that you need to cut. Some of this is why many of us just build an oversize machine to handle any size job that comes along. Two small circuit board machines can probably be made for less additional money than one large machine will cost.

CarveOne

[LazyMan]

I guess it all depends on the size of your machine and how you define high speed machining. If your idea of high speed machining is like this http://www.datrondynamics.com/ then 100kg really is not heavy.

To really give a much better answer though we would need to know the specs you are trying to achieve such as feed rates, accuracy, materials your trying to cut.

[Swiss]

Hi guys, thanks for the replies.

CarveOne, the machine is not for routing PCBs. It's for machining Delrin and Aluminium parts for our robot hands.

LazyMan, that Datron machine is exactly what I have in mind! In fact, a guy from Datron is coming to visit our workshop on Friday. What I'm trying to do is prove we can build a better machine for less money.

The Datron M75, which is the smallest and cheapest one they do (only just fits in our workshop) has a granite base, 30,000rpm 1.2kW spindle, 14m/min speed. Work volume of 520x520x240mm. Ballscrew drives for the axes. 10 station tool changer. Footprint of 1.3m x 1.3m. Price tag £40,000.

The machine I'm spec'ing is similar: Granite base, 30,000rpm 2.2kW Colombo spindle with ATC, 20m/min, same work volume, Aerotech brushless linear motors for all axes, Renishaw 1um encoders, laser tool height measurement, THK linear bearings. 18 station tool changer. Footprint 1m x 1m. I would like to achieve an accuracy of 10um. The largest tool we currently use is 4mm dia.

All the parts plus labour comes to less than £30,000. We have a professional machine builder who will assemble it for us.

Hugo

[LazyMan]

Looks like you guys are building a pretty serious machine. Please show us some pics when its done if your allowed by your company! I have dreamed of building a Datron style machine for a long time. About how much labor was done in house?

Your robotic stuff is very cool. The air muscle is very interesting.

[Swiss]

If we're done. I have yet to convince by boss that a) we can afford a new machine, and b) it's not madness to build a custom one.

About how much labor was done in house?

Well, none yet, but the idea is to get the granite done by a company like Precision Granite. They can attach the rails too. Any other high precision parts would be sub-contracted, and any remaining parts would done on our Emco Concept Mill 105 (rubbish, don't get one).

[CarveOne]

Originally Posted by Swiss Hi guys, thanks for the replies. CarveOne, the machine is not for routing PCBs. It's for machining Delrin and Aluminium parts for our robot hands. -snip- Hugo

I guess I just just assumed that from the link at the bottom of the post. The robot hands work is cool.

CarveOne

[jdr]

Hugo

Start with this 4 axis machine and add your spindle, etc.

Less than $2,500.00

Link:

http://cgi.ebay.com/Anorad-4-Axis-Pi...item20af58b631

Also, a few months ago on USA Ebay a lister had about 8 of these in England for around the same price.

[Swiss]

jdr,

Wow, that's an amazing price! It's very tempting. The only thing is that it's a little small.

Hugo

[LazyMan]

I don't know if you have come across this epoxy granite machine casting thread. Its very long and has lots of information.
http://cnczone.com/forums/showthread...t=epoxy+granit

Along the thread there are some pictures of some machine castings people have done.

It even has an index for it
http://cnczone.com/forums/showthread.php?t=38800

[Swiss]

I've been keeping half an eye on that thread, which is hard because it's so big. I've even spoken to a guy who does epoxy granite castings professionally. But, in the end, I think it's just much more complicated than solid granite. Notice that there are no 300+ page threads about 'phoning a granite cutter and ordering accurately lapped cut blocks. They're not even that expensive. Plus I need to convince my boss that this is a zero risk venture.

Still, the idea of just casting some more complex pieces all in one go is very tempting. Perhaps if this build goes well we can try something more complex.

Hugo