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Hi from Perth Australia
krv3000:
hi and welcume
howsitwork?:
Hi and welcome to the play pen!
PK:
--- Quote from: PekkaNF on July 05, 2015, 08:57:24 AM ---Really mad at you not showing this stuff before :poke: :poke: :poke:
--- End quote ---
See the problem is that this sort of work is addictive, which is fine, but I only got into CNC to help make more rocket bits:
But I got hooked.
Years later I finally plucked up the courage to admit I had a CNC addiction and went cold turkey.. I left the site idle for years and it expired.
--- Quote ---But I could calmn down fast if you would tell me more about the gripper on this page:
http://www.caswa.com/cncathome/spindles.html
Got some anecdotal information, but few things were not evident to me.
* Is that taper more or les SK15?
--- End quote ---
Its just an 8 degree taper, no idea who else uses it.
--- Quote ---* Can I have dimenssions of the gripper collet and pull stud?
--- End quote ---
Tough, I don't use that spindle any more. On a scale that small, I found the plain shank toolholders worked better.
Those are 8mm shanks.
re the studs:IIRC the heads of the studs were 5mm diameter.
--- Quote ---* How does it work?
--- End quote ---
There's actually some deceit on that page (not everything you read on the interwebs is true you know).
The cad model shows a complex arrangement with three leavers and an o ring opening them.
With that spindle being so small, I got better results by making the claw look a lot like a tiny R8 collet with a groove just inside the nose to grab the stud. Then I bent the collet open and hardened it. Pulling on the drawbar would then close the thing around the studs.
--- Quote ---* How much is the griping force? You probably had some some figures in mind when you were planning taper/force. Care to open a process a little?
--- End quote ---
Short answer, not enough. When you get that small, the overhead bits (pull studs, claws, springs etc) start taking up disproportionate amounts of room. That room comes off your friction surfaces and you loose grip.
Another bad bit is that the pull stud setup requires quite a lot of precision and hardened, high strength parts. I ran the plain shank ATC for about a year with a soft collet.
Finally though, when we started using the little router for production work, and employee cooked the magnets off the servo motor driving it. This triggered us getting our first water cooled, 24KRPM spindle. For a small machine, with a high resonant frequency, these are just the ducks nuts. I'm talking 6-10 times the metal removal rate. I'll be putting up a page specifically on them.
--- Quote ---Really liked the stuff you do. Enjoyed reading about X3 and ELS. "Spindle speed control for the mill" did not reveal me of it's secrets.
--- End quote ---
TA, not much to say on the DC motor drive, you can just buy them for next to nothing these days...
Cheers
PK
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PekkaNF:
Scary looking stuff those rockets.
Thanks. Great info. While experience replaces nothing, nothing replaces first hand experience.
I have been drawing/toying (design is big word) some power bar or semiautomatic tool change. Not really into ATC, but some sort of quick change would be in order. Taper and retention force are variable that we can play with. Self releasing taper needs more force than MT.
I have seen three main DIY gripper designs: Balls, spring collet and lever style. They are very different and each has it's issues. Lever type seems to be only real choice with self releasing taper. You are right, all parts needs to be carefully designed and preferably heat treated (all my small bar stock is tempering steel, I can build parts out of this and anneal or harden them, but small parts only).
You also had interesting QCTP mount spindle:
http://www.caswa.com/cncathome/images/spindle_toolholder.jpg
Care to tell about motor power/rpm and what is that spindle good for? Looks like a 100W brush DC-motor?
I have tried dremel (not worth of unless you have nerves of budhist monk), I have Proxxon BFW 40/E which I think is a bit of a toy in performance and pig in size:
http://www.axminster.co.uk/proxxon-bfw-40-e-mill-drill-system
I was in process of putting an 3 phase AC motor with vector drive to get close to right rpm with belt drive, when I got slightly off the track with PM AC servo, less than 1/2 the size and more rpm, but I had stability issues (AC servo and old inverter).
I have been reading some stuff on BLD motors, but haven't been able to nail the motor/driver combination. I don't want to go RC stuff, and can't bring myself to pay real brand servo prices. Probably will build two. One rough one for drilling 2-6 mm dia holes and realatively low rpm and other with collets and high rpm. I like belt drive, gets the motor away from spindle and easier to align.
Pekka
PK:
--- Quote from: PekkaNF on July 07, 2015, 10:15:19 AM ---I have seen three main DIY gripper designs: Balls, spring collet and lever style. They are very different and each has it's issues. Lever type seems to be only real choice with self releasing taper. You are right, all parts needs to be carefully designed and preferably heat treated (all my small bar stock is tempering steel, I can build parts out of this and anneal or harden them, but small parts only).
--- End quote ---
Seriously, go with plain shank toolholders. Maybe take a look at how Tormach do theirs. They reference in Z against the spindle nose, so you can still use tooltables. My preference was just to measure tool length every change. I hate tooltables....
--- Quote ---You also had interesting QCTP mount spindle:
http://www.caswa.com/cncathome/images/spindle_toolholder.jpg
Care to tell about motor power/rpm and what is that spindle good for? Looks like a 100W brush DC-motor?
I have tried dremel (not worth of unless you have nerves of budhist monk), I have Proxxon BFW 40/E which I think is a bit of a toy in performance and pig in size:
http://www.axminster.co.uk/proxxon-bfw-40-e-mill-drill-system
--- End quote ---
Yeah, its a bit of a dilemma. The requirement is for a small powered head that fits on your toolpost and can drill big holes.... Hmmmm. To get the performance, you need something about the size of an Seig X2 head, Which is too big. So you go small and fast, which means small cutters and chatter..... Dremels are a classic example of how far marketing can take a bad design. The overhang from the bearing is enormous. I've heard good things about the proxxon.. When I've really needed to get jiggy with a toolpost spindle, I've ended up with a trim router. Noisy but effective up to 1/4" cutters... To answer your question, the motor was about 150W. But driven by an O ring on those little pulleys, I doubt it could transfer 100W.
--- Quote ---
I was in process of putting an 3 phase AC motor with vector drive to get close to right rpm with belt drive, when I got slightly off the track with PM AC servo, less than 1/2 the size and more rpm, but I had stability issues (AC servo and old inverter).
--- End quote ---
I reckon you're on the right track with the FVD. Fractional horsepower 3phase motors still tend to be quite large though. Brushed DC is really the best power density per buck at low RPM's maybe add an encoder and run it from a Gecko DC servo drive.
As you've figured out, adding an encoder gets you a brushless servo which can deliver high torques at low RPM's for medium bucks. IIRC I bought a 600w Servo for about AU$650 landed a year or so back.
Have you considered a little high speed spindle? I just bought a 60KRPM 350W job. Its about 48mm diameter... If you go to 80mm you can get 1Hp at 24KRPM. Simple, but limited to small cutters...
PK
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