Accurate Strong Gantry

[Ross77]

What size cutters are you planning to use in alu? 50mm face on plastic wont generate much force.

Welding is you are all probably aware is an art in its self and you must only weld small sections at a time and move around the frame to reduce heat build up. Its slow but the only way to go.

You can design to minimise joints and increase contact area so spot welding can be used.

Is your model in AutoCAD? If so I could help out with the frame design. Hopefully increase strength and reduce the weight! :0)

[vargai]

What size cutters are you planning to use in alu? 50mm face on plastic wont generate much force.

Welding is you are all probably aware is an art in its self and you must only weld small sections at a time and move around the frame to reduce heat build up. Its slow but the only way to go.

You can design to minimise joints and increase contact area so spot welding can be used.

Is your model in AutoCAD? If so I could help out with the frame design. Hopefully increase strength and reduce the weight! :0)

I have downloaded some kind of study about machining force and my
goal on 1000 N is not oversized requirement. I hope I can use max DIA 10-12 mm with moderate technology and dia 30-35 face mill on same way.
The machine will give the right answer and I will give a "reluctant" acceptance to it. I do not care if some work take a while since I will use this machine on one off and small batch production. With good strategy and preparation I even can compensate it but not bother if not. I have a day time job so it will be a free time profitable passion.
Regarding the design I am rather analyst type and it is important and challenge for me to see the theory behind the result.
Everything happens according to some kind of theorem and if one catches the rule then catches the physical result.
So thank you for your help in advance.I still have to adjust my plan a bit and revert it later.
I use Solidworks but the estimating the elastic deformation (strength ) would be a big help too.

[Ross77]

Could you post a link to that cutting data? Some quote the force required to cut the material and the tangential force seen by each axis can be much lower. Those figures seem a bit high. Unfortunetly all my reference material is on my old pc so will have to dig it out.

What spindle do you plan to use? To a certain point the more powerful the spindle the lower the cutting force.

[Boyan Silyavski]

http://aluminium.matter.org.uk/conte...eid=2144416345

Its very difficult to say the exact cutting force, having in mind it will vary with your tool sharpness, type, teeth count,rake angle,the type of aluminum, feed, rigidity of the machine.


Better use your common sense. Download and use the spread sheets here from the forum to calculate the machine stiffness at different points, use HSMAdviser or GWizard to calculate spindle HP and deflection at different settings. Make up your mind and choose what to do further.


But i still don't get why you dig so deep. Its so simple. You want to do all up to aluminum- make a router. You want to do iron, steel and so - make mill. Once you decide that, its a matter of choosing the design that fits you and realize it.

I don't see reason fitting mill head to router. Cause once you start that, you will finish with a mill.



Your initial design was spot on. Your gantry was weak. Fit a gantry similar to my second build/i am doing right now/ and i assure you you will reap through aluminum like butter. The yellow router i build /look signature/ reaps through 1mm of aluminum without turning on the spindle , like a knife passes through butter, without feeling it at all. Or follow Johnathans design where the gantry is split in 2 and the z is inside. That are proven designs that will work very well. A well build machine will hold better tolerances than cheap chinese mill.

You will very unlikely use 12mm bits with aluminum. Most possibly 3mm and 6mm. Cause aluminum is expensive to waste it with 12mm tools.


Not that i don't believe that for a first build you will not make it. I just know how much time a very good design needs. Mistake here and there will cripple considerably the capacity of the machine. Talking about machine made for metals i mean. Aluminum or no. I for once want somebody to make the mill as i envisioned the column in the suggested post. If you feel confident build the mill, it would be cheaper than suggested if you build the frame yourself. Hell, once i finish that big trunk i am building now, will build myself a mill.

[vargai]

Its so simple. You want to do all up to aluminum- make a router. You want to do iron, steel and so - make mill.

Give me a little time to get my act together.
I have no the total budget now so step by step building. I could buy a pile of steel here Hungary for 2500 GBP so buying used machine is not my way.
This is not a summertime love with a Spanish Bonita and I am too old to make mistake.I have machined and built an A3 format router with TBA drive two years ago and I would leave out some steps and would like to build this 1000x700x300 mm real machine.That's why I am perhaps too careful.
So to spill the beans : my intention is with this build beside the passion and joy for me and my sons is to make some kind of retire fund. In this I trust better than in Gov.
I can get jobs form my employer since we mainly do automation projects with cabinets and software but the give the machining to subcontractor for high price.
Regarding to the other job source as well I do not want to narrow my flexibility only to Al, plastic.
So let's say mainly Al, and plastic but with passable capability in steel.
I have used this word "steel in my introductions but I left it later seeing this is taboo at router.
When I look at the machining forces in the above post I think with 1000N one can provide acceptable performance in steel too acknowledging that this is not an intensive material removing machine.
Building a frame with resistance to this forces not impossible challenge and I am sure your yellow one is pretty stronger. Still believe in the above size the fixed gantry with improvement fits to my goal but I will study yours and Jonathan's .
As you pointed to it I am rather confused about the spindle but I have to draw the borderline soon.

[Boyan Silyavski]

The bottleneck of this project will be the spindle. So a certain realism should be applied when designing the machine.

Why? I agree that you could build a frame any style for a mill. And make it rigid enough.

You have exactly 3 general choices:

-use cheap Chinese water cooled spindle up to 3kw /2 phase/ or even bigger 4-5kw. 18-24k rpm. The problem is that the bearings of the spindle are not made for steel machining though from time to time you could do that. No low revolution power. I would never try to use mine spindle on steel

-Use the BT30 spindle 8000RPM from ali express. Now this spindle screams for column Z. Otherwise how you will mount the motor and the tool change and balance the weight? Not possible. Not so cheap though as only the spindle side will be >2000eur with the motor and changer. Not so fast for High speed machining


-use the design like the german gantry machine example and add bigger than 10kw spindle. That will work best for what you want but the spindle will be very expensive.


So as you see, it is like i said before- you want steel -you make a mill, you want up to aluminum -you make a router. You want both-yes it possible, but prepare some $$$, cause you will need BIG motor to be fast and at the same time to has power on the low rpm.

[JAZZCNC]

I agree 100% with everything Boyan says regards spindle but it just doesn't stop at the Spindle to do this correctly.

The massive build required to cut steel correctly with acceptable accurecy and repeatabilty affects the linear motion and motors used plus many other things. (Has Boyan knows well.!!)
Wood's plastics etc need higher feeds to cut correctly so this means motors which can handle high Mass of heavy gantry and still allow higher feeds.
This will mean servos to do it correctly. Servos require high pulse counts so this means quality motion control cards and control software. The list and expense goes on and up.

Has Boyan will no doubtly be very aware of this quickly gets expensive and requires more attention to detail and selection to get it correct.
Even then there will always be a compromise in the machine some where.? One machine can't do everything to high standards without being very very expensive.

IMO you will be much better building a router that will cut everything in it's capabiltys, Ie woods,plastics etc to a high standard.
Then buy a milling machine at later date that will do and give the same high accurecy and repeatabilty with Aluminium and Steel etc.

The chances of failure or dissapointment for large machine to cut steel is very high and the extra expense trying to do so easily wasted. Much better to be realistic about this just build a strong functional router and save the money you WILL waste trying to build all round machine then put it to buying a milling machine.

[vargai]

-Use the BT30 spindle 8000RPM from ali express. Now this spindle screams for column Z. Otherwise how you will mount the motor and the tool change and balance the weight? Not possible. Not so cheap though as only the spindle side will be >2000eur with the motor and changer. Not so fast for High speed machining

I have just went through the sites of motor, spindle, etc and they are expensive even from China.
Ie.only a BT40 spindle would be 2000 EUR in my hand with VAT,etc.
In my present eyes it is too much for 30 kg engineered steel and if I went with this I would make it myself.
Regarding the power I think I would satisfied with about 4 kW
But the main issue is not this and thank you to summarized.

[vargai]

Could you post a link to that cutting data? Some quote the force required to cut the material and the tangential force seen by each axis can be much lower. Those figures seem a bit high. Unfortunetly all my reference material is on my old pc so will have to dig it out.

What spindle do you plan to use? To a certain point the more powerful the spindle the lower the cutting force.

Thank you to correct me. I have just referred to it by heart and of course do not want to propagate false data
Here is the link and it says 40-50 N
http://www.ijens.org/103004-5151%20IJBAS-IJENS.pdf it is talking about HSM milling but use 1000rpm for this test ??

200-400 N is from a college measurement protocol where the matl is mild steel
the first is 10 mm flute mill



and the follow is face milling in mild steel



Sorry for digging too deep but I am confused about the new present day parameter used in Ali.
At my former job we machined Ali 20% of total and used empirical values in technology heard from colleagues and the owner of the shop. On that Hurco VMC we used max 4-5000 rpm (4-12mm 2 flute cutters) and as I see this is the lowest on router. Could you tell some practical values according to table above? It is not complicated but I am not confident in machining calculator but more familiar with practical data.