Designing small VMC 3/4 scale VMC 15

So ill update this as i complete the CAD drawing but ive been looking at buying a VMC but im cheap. So i started thinking maybe go the china route like LCVETTE did but he has an actual production need. I just do some small one offs for my brothers company and my current mill handles that fine. This will be a practice of drawing every bit in cad then ill calculate costs and if it comes out under the cost of a used VMC of the same class then I will proceed. I may do it even if the costs are higher just to have built the machine. My other option is to convert a RF-45 to cnc but by the time i add linear rails and whatnot i think the cost will be about the same unless i can find one used for dirt cheap (doubtful) and still nothing but crappy tts for an atc.

So my goals are:
Keep cost reasonable
Be able to have slide ways machined on my current machine (I can coax about 24"x40" i think but ill have to reverse the x axis motor.)
Be able to cut 12"x12" plate minimum
Needs to be fast 400ipm rapids or so
Needs to hold .001"
Well designed to fit everything well
To learn how to better design structures and the small details
Off the shelf components
Rigid machine
30 or 40 taper machine i want readily available tools plus my current machine is a 40 taper
No more mach 3
Complete weldament machine (so far ive been able to keep this up) but i have to be able to weld it with my machines
Not my goal so much but a selling point if i end up needing a more industrial machine is keeping it under 2000 pounds (i think it will finish right at that with control etc)

Other things
Alot of the bar stock sizes and whatnot i use are what i have on hand. so far ive kept it as only weldaments

This machine is designed by me. I did use some of Fadals ideas but i didn't take any measurements besides looking at pictures and doing some basic referencing (I have never seen one in person) just saw a manual. I am guessing that the main tube on a Fadal is 16" and mine is 12" so that is where the 3/4 scale came from. I admit that their way cover ideas were ingenious and i may have borrowed that. I didn't have much to go off either there isn't much out there on these vmc15s.
What type of cad files do you guys like? for now ill post a picture of the main assembly i have so far.

I use Solidworks for modeling if anybody cares

Spindle:

I considered using a tormach pcnc 1100 spindle but theres no ATC capability on the 30 taper model so i found these spindles on ebay and alibaba that are bt30 with pedal clamp for around $700 so thats probably what ill design around. considered just using the pcnc 1100 head casting too but if i can make the saddle weldament ill be able to weld up a head.

Fabrication:
I plan on stick welding pretty much everything together and later ill decide on whether ill send it to get normalized or if ill get two of the grass burner torches and just do a good post weld heat. I think the welds will have to be pre heated (about 400 f) i think so that would be the easiest time to raise that temperature up to normalizing temperature (900-1100 degreesf)

Equipment:
I have a large lathe 14x54(19" actual swing 14" is over the cross slide lol)
Decent size mill its a Spindle wizard excello 602 retrofitted by me.
220 amp mig
175amp dc tig/stick
6x18 surface grinder
decent size bandsaw
all sorts of other tools

Travels:
I said what i wanted in the beginning but it looks like so far ill be getting about X18" Y14" and Z24"
the z I am still not sure on as I have yet to design the spindle mounting plate only the beginnings of the column. the X and Y and mostly finished pending some minor modifications to what rail size (id like to use standard sizes) The table is 18"x12" and i think ill have to get this piece cast and ground from china but thats long in the future

Control:
Gonna try Linux cnc with Gmccoppy on my other machine so well see how that goes
Planning on a set of mesa cards if i decide on the linux


Lastly bear with me I am active duty military so don't expect to see this machine in 6 months it could take me a year or three. Plus i am in the process of having a new shop built back home so that will take priority over this and ill only be messing with actual construction when I am back home on leave. Therefore i have loooottss of time to fully learn to design every aspect. Hopefully i get a good response from you guys to keep me motivated and answer my thousands of questions.

http://www.cnczone.com/forums/attach...d=377360&stc=1

I'm still continuing the design but I'm have a lot of trouble designing a head that will easy to build but is also strong and spaces the spindle nose down a bit for atc capability currently it seems like it might work but I'm not quite sure because the Chinese dimensions are not very specific.

Along with that I'm trying to determine what kind of motors to use. The spindle I am considering the use of an ac servo because they are cheap from china and a 5hp one could be had for about $600. Or I could go with a standard motor and vfd but I'm not sure about minimum and max Rpms that's another situation that I don't know what will work better. I would appreciate if somebody had a rough guide for that. I'll be putting a vfd on my other mill and that info would really help me out.

Axis drive motors I want to be 750watt ac servos but that might not be enough acceleration to get moving as fast as I want. So maybe 1kw would be better. If you guys have a good motor calculator that would be great. Also maybe considering brush D.C. Servos for their ease to get and drive compatibility. Not to mention I have 4 of them around 2hp and a set of dgs2 drives but In this being a fresh design I'll stick to ac servos for now. The plan is 1:1 coupling but I can use a 5mm or 10mm pitch screw.

I'm not the right guy to help with choosing a VMC but, out of interest, why do you care if the Tormach 1100 spindle head doesn't support ATC with their 30 taper cartridge?
I.e. What is wrong with just using the R8 spindle it comes with instead? They offer an ATC option for that.


You mentioned that your goal with a 30 or 40 taper spindle was readily available affordable tooling. Doesn't an R8 taper spindle also offer this? You also mentioned that you were cheap. Their BT30 cartridge costs extra. The R8 is standard.


BTW, there is an eBay seller offering (relatively) low cost ATC BT30 belt drive milling spindle cartridges with the pneumatic drawbar accessory for around $1,000 plus $200 shipping.


I believe the company that makes these Chinese BT30 belt drive diy spindles is called Skyfire. They also sell complete CNC mills in various sizes. I have no idea how the prices or quality compares to Tormach though.


Some of these Chinese vendors seem to price their products too high for the American market without checking out the competition first. Personally, I would only consider buying anything from China if it is materially less expensive than comparable US or European made products after all shipping and import costs.

Quote:

---

Originally Posted by Goemon

I'm not the right guy to help with choosing a VMC but, out of interest, why do you care if the Tormach 1100 spindle head doesn't support ATC with their 30 taper cartridge?
I.e. What is wrong with just using the R8 spindle it comes with instead? They offer an ATC option for that.


You mentioned that your goal with a 30 or 40 taper spindle was readily available affordable tooling. Doesn't an R8 taper spindle also offer this? You also mentioned that you were cheap. Their BT30 cartridge costs extra. The R8 is standard.


BTW, there is an eBay seller offering (relatively) low cost ATC BT30 belt drive milling spindle cartridges with the pneumatic drawbar accessory for around $1,000 plus $200 shipping.


I believe the company that makes these Chinese BT30 belt drive diy spindles is called Skyfire. They also sell complete CNC mills in various sizes. I have no idea how the prices or quality compares to Tormach though.


Some of these Chinese vendors seem to price their products too high for the American market without checking out the competition first. Personally, I would only consider buying anything from China if it is materially less expensive than comparable US or European made products after all shipping and import costs.

---

The reason to not use r8 spindle with Tts is because it cannot handle much horsepower or large tools until you get pullout issues. A 30 taper will easily take 5hp vs the tts that will have pulled out or spun. The reason to not use tormachs 30 taper is because it has no capability for an atc with the way it is designed i.e. Never an easy way to add a pull stud and gripper arrangement. An atc is pretty much necessary for any real vmc if I don't need atc my mill now fulfills that pretty well.

That spindle you speak of is what I think I'd like to use but I have no idea on quality and I've seen them from tons of sellers from about $650 to $1200+ with some accessories like a air cylinder. Not much as far as reviews around for them either. I found a Russian video showing the runout and maybe 1 or 2 other mentions but relatively nothing. I'd think the guys around here would've given them a try. If you find any info please enlighten me.

Sorry I don't mean to disregard everything you said it's just I don't think the tormach stuff is strong enough for my wants although it is a good price.

I found the same problem with a bunch of those Chinese belt drive milling spindles on eBay. There is little to no real info or reviews anywhere.

I guess a person just has to accept the risk if they buy one of those things.

I wish there were better options available from the American stores that already sell other Chinese spindles. For example, stores like Automation Technologies which sells high speed chinese spindles and low speed milling motors but none of the Chinese belt drive spindles. Maybe they know something we don't.

I was not able to find any other low cost belt drive milling spindles capable of supporting powerful motors or higher speeds. For anything beyond what Tormach sells, there was a huge jump in price.

Maybe ordering one of those BT30 ATC units through eBay is worth the risk. There are no other low cost options and eBay at least offers their money back guarantee if they send you a broken one.

Quote:

---

Originally Posted by Goemon

I found the same problem with a bunch of those Chinese belt drive milling spindles on eBay. There is little to no real info or reviews anywhere.

I guess a person just has to accept the risk if they buy one of those things.

I wish there were better options available from the American stores that already sell other Chinese spindles. For example, stores like Automation Technologies which sells high speed chinese spindles and low speed milling motors but none of the Chinese belt drive spindles. Maybe they know something we don't.

I was not able to find any other low cost belt drive milling spindles capable of supporting powerful motors or higher speeds. For anything beyond what Tormach sells, there was a huge jump in price.

Maybe ordering one of those BT30 ATC units through eBay is worth the risk. There are no other low cost options and eBay at least offers their money back guarantee if they send you a broken one.

---

Yea and I probably just have to take the risk like you say. If I have too I could always put new bearings in and regrind the taper. But that's far enough in the future that I'm not too worried yet.

I guess the alternative is adjusting your requirements to give yourself more local and reliable options.

I don't know what your requirements are but for hobby work, you might be able to get by with far less horsepower than you think.


I saw some guy on YouTube milling stainless steel with a fairly asthmatic 1.5kw high speed CNC spindle. This thing had nowhere near the torque or stiffness of Tormach 1100 or 770 spindle heads but the result he achieved looked fairly good (considering what he used).


I guess it comes down to how fast you need to turn out parts.

Have you looked at the Daytron high speed CNC mills? It's a good site for inspiration and education.

Sounds like you want to build your own machine, but I think you could come out money and machine capability ahead if you customized one of the SkyFire machines. Beef up the identified weak areas, and you could be running in a few months...

Well just like lcvette I ended up buying a machine because after I made drawings and saw costs it was cheaper to buy.

Ended up grabbing a 1999 fadal vmc 15xt.