[ihavenofish]

Chinese newyear takes a little bit longer then dutch new year, lol. But received the package with the HSAC linear guides last friday.
All looks good and was packed in a a strong wooden box.

we don't have mandated holidays here anymore at all. a lot of stores are open xmas day and new years day. in china it seems to be a more serious affair. the whole country shuts down for several weeks.

[handlewanker]

Hi, just to let you all know, my last communication with Defeng was on the 18th Feb and I asked for the longer rails and ball screw to be added to the mill package so that I could do the column extension modification that I talked about previously at a later date.

I will still have to make and fit the support block behind the rails on top of the column and for the remounting of the longer ballscrew, but at least I get the rails and ballscrew included in the packing case with the mill without having to incur separate shipping costs etc.

The other thing I mentioned previously was the modification to the draw bar, and initially I will still use the existing draw bar with Bellville washers, and will compress the washers with a lever and stepper motor combination......the stepper motor will pull the end of the lever down to release the tools etc......I don't like the idea of an air cylinder on top of the head and also the need for a compressor to have air for the cylinder, so a stepper motor with the necessary grunt is all it takes.

As the forces for the compression are unknown (to me), I'll have to wait until the mill arrives to see how much force is needed to depress the draw bar, but I expect that a lever/cam design with a 10:1 ratio will enable a beefy stepper to push the draw bar down without getting too hot under the collar......it's only a very short duration action so no problem with overheating is envisaged,

I'll probably have a stepper motor with a bronze nut on the end of the lever to do the pushing for tool release.

This is a temporary set-up, as I have a design for a power draw bar that does not have Bellville washers for the holding force.
Ian.

[ihavenofish]

a 2mm lead acme screw / nut and 280 oz nema 23 stepper should have the power to push the drawbar with no lever - it should be well under 1000lbs. a limit switch at the travel extremes will safeguard against a stall - although I understand you'll only be manually swapping tools so its not too big a deal.

if you did do a 10:1 lever, you could just use it by hand.

[handlewanker]

Hi, there you go, when you design without having the specs of the thing you're designing for you get carried away with force requirements to be overcome.

Thanks for the info on the stepper Avno, being totally new to this lark (CNC) I tend to over engineer in case the forces are more than anticipated.

I should have done the research first for the stepper motor torque to push down 500 kg using the screw thread as applicable.

A direct drive against the end of the draw bar top end to compress the Bellville washers would be simple to achieve, so I might go that way and be done with, although my first intention was to have a system without the Bellville washer set-up.

I don't think I'll ever be working the spindle to such a degree that the Bellville washers would not hold the tools in the spindle taper.

I just have to wonder if a ready made linear actuator is available off the shelf with enough force to directly push the draw bar down, which would simplify the build instead of re-inventing the wheel and making one etc.

Now that Skyfire has the ISO 20 spindle in the catalogue options, the next logical step would be to also have a linear actuator available ready to mount on the top of the SVM-0 head when that spindle option is chosen......the mounting bolt holes for the actuator would need to be in the head casting top anyway at the manufacturing stage, and would depend on the design and mounting method of the actuator.

Going to an electric linear actuator makes the need to have compressed air for a pneumatic cylinder unnecessary, and is much simpler to achieve even for a DIY approach.

This would need a simple but necessary modification to the mill, to add a few extra bolt holes, and would not need a redesign of the head at all.

I think the actuator could remain in place on the head if/when a high speed spindle is used in place of the ISO 20 spindle as the spindle change over could be accomplished by removing and inserting from the bottom of the head casting after the bolts in the split are loosened.

To my mind that would be a complete package with nothing further to add.
Ian.

[handlewanker]

Hi, just had another thought....if I have to design/make a linear actuator I would go for a small ball screw drive and a 12 volt geared DC motor to move it,

Small geared DC motors giving tremendous torque are available on EBAY for a few bob, so I might cost up that option too.

I would be thinking in the region of an outlay of $50 at most for the screw and motor to make a linear actuator for the purpose.

labour of course would be DIY and so free.

Design time.......the drive must provide at least 500Kg and move at least 30mm......I think the draw bar only needs to move 6mm to clamp and unclamp the tool, the rest is clearance, but that's just a guess.

It will be with a moving ball nut in a tube with guide slots etc, or something like that......a ball nut will give a long and trouble free life as opposed to a bronze one on Acme thread.

It's probably already been done before, but I've not seen it, and it will have to be custom made to fit on the SVM-0 mill.

Going down this path is against my desire to get away from Bellville washer clamping, but when all things are equal the simplest solution is always the best policy for efficiency.
Ian.

[ihavenofish]

Design time.......the drive must provide at least 500Kg and move at least 30mm......I think the draw bar only needs to move 6mm to clamp and unclamp the tool, the rest is clearance, but that's just a guess.Ian.

release throw is 5mm so 10mm of motion should be plenty. the bellevilles are high tolerance. they will always be in the same spots clamped, unclamped, and with no tool. as long as the whole unclamper can be popped off for access, youll be fine.

[handlewanker]

Hi, only 5mm......that's good news, makes the mechanism for the move a lot more simple.

I don't think the linear actuators currently offered in the market are such a good idea after all.....all of them on EBAY have very long travels.

I see another poster on a different thread is marketing a linear actuator type power drawbar for the Tormach (maybe Novacon?) so the idea of a linear actuator is not new.

I am thinking of a cam/roller type mechanism instead of the linear screw type, positioned directly above the draw bar end that rotates 180 degrees to move the drawbar, and a stepper motor of even modest strength would suffice for this design.

Moving in a rotating motion means the mechanism is extremely simple and with a throw of only 5 to 10mm the force to compress the washers with a cam will be easy to achieve.

The cam would be mounted with a bracket on top of the head and with the stepper at 90 deg to the spindle it will be positioned sideways to do the rotating and have the cam directly mounted on the stepper spindle......it could also be working against the end of a lever if more force needed, but I think that would be overkill.

The beauty of the stepper drive means it can be rotated precisely 180 deg and be held there with the cam at bottom dead centre so making the mechanism self locking during the tool changing.

Some switching circuitary design will be needed to ensure the stepper rotates and cuts out at the 180 deg mark.

This will make the power draw bar extremely simple and controllable at the touch of a button (or under Mach 3), and being electrically operated also makes it applicable to ATC should that need arise.

I think that ATC can be very easily achieved with a simple static table end mounted magazine and this type of power draw bar without having to go to rocket science design technology, and a magazine with 9 tools in a 3 X 3 mount will cover most needs.

The tools are all ISO 20 type so the diam of the collar will not make the width of the magazine too big, and a magazine of 3 x 4 will give 12 tools which is a huge collection by any description, provided the extra weight on one end does not impinge on the ability of the table to move easily.

ATC may not be something that most will need, but for those that would like to automate a process, it could be quite simple to achieve.
Ian.

[ihavenofish]

linear actuator is the standard. either air or hydraulic. mechanical ones work too, but they wear and generally cost more (assuming you own a compressor already).

I actually saw some gear motors with lead screws at a local surplus store this week. no idea if they would have the strength, motor was tiny. maybe 3-4mm lead (1/8" most likely).

look up mcmaster.com for linear actuators - they carry almost everything you can imagine. find the best suited one, then try to find a good price somewhere else.

[skillalot]

Dude, why so much trouble? Just get a big air cilinder on top and you're done.
Eventually you will want to buy a compressor anyway to clean your parts from cooland and chips before you take it out of the machine.

[ihavenofish]

Dude, why so much trouble? Just get a big air cilinder on top and you're done.
Eventually you will want to buy a compressor anyway to clean your parts from cooland and chips before you take it out of the machine.

or run a mister. or venture vacuum jig, etc etc.

[handlewanker]

Hi, nope, air is not on my wish list for a power draw bar, although I have an air compressor I don't want to go down that path.

I like the idea of a stepper motor driving a cam directly on top of the draw bar, and that is what I'm designing now.

Having an all electric set-up is the way to go as far as I'm concerned and the design is quite simple.

I shied away from a manual lever to depress the draw bar as it means the head will be pressed down when the draw bar is pressed down.

It needs 500 Kg to depress the draw bar Bellville washers and even with a 10:1 lever advantage you'd still have to put 50Kg on the lever end.

Having the stepper driven cam in bearings on either side of the draw bar will contain the forces to that area and the design "could" lead on to ATC although that is not the prime reason for that design preference, it's just a spin off.

My original thought path had a 10:1 ratio lever with a bronze nut on the end and a geared motor driving the end of the lever up and down.

A 12 volt 200 rpm geared motor has massive torque when it's geared down to do the pushing, and as it is on a 10:1 lever the force would be more than adequate.

12 volt geared motors, similar to those used in drill drivers, cost about $10 on Ebay, but I did not like the idea of a bronze nut and screw drive, so the cam and stepper appears to be better........at least it's completely DIY and with a minimum of machining ops.

It's on my Ipad at the moment so the design is evolving as more ideas come together.
Ian.

[miljnor]

Some people love doing things the hard way!

More power to you, stick to your guns.

Although most commercial machines use air power draw bars in the shape of a large piston!

I'm interested to see what he comes up with.

[hive8]

anyone heard of Defeng seems i cant get a hold of him anymore, I do have some orders for him.

[wizard]

anyone heard of Defeng seems i cant get a hold of him anymore, I do have some orders for him.

I would expect that he is in catch up mode right now, just like any other business after a long holiday. As for communications are you using this address: [email protected]? Skyfire has a nice web site that is still very active.

I'd continue to try to make contact, there is a good possibility that he is simply swamped with work. So far the machine have been well received and as such I can imagine a big demand.

[engnerdan]

There are a lot of posts here and I have not got through them all. So I apologize if I missed it. But has anybody purchased a mill from Skyfire yet? It looks like his bigger mill in this thread is exactly what I am looking for.

Dan

[handlewanker]

Some people love doing things the hard way!

More power to you, stick to your guns.

Although most commercial machines use air power draw bars in the shape of a large piston!

I'm interested to see what he comes up with.

Hi, far from being "the hard way", any power draw bar requires work of some description to make it work and not wear out prematurely.

I am working on a pure electric design to offset the need to have a compressor and big air cylinder, although the industry uses that method, they have air on line all the time so that is what they go to.

In it's simplest form the draw bar can be depressed with a simple lever to get the 5mm travel to release the tool, so the stepper driven cam does just that, it rotates the cam on the draw bar end and does the necessary tool release at the touch of a button.

There still has to be a mounting point above the pulley to attach whatever mechanism is used, be it an air cylinder or a cam and stepper motor, so that is just design......and it will suit any machine that uses Bellville washer draw bars for the retention force.

I think even a windscreen wiper motor could be used to turn the cam as it already has a worm drive gearbox on the output to get the slow speed of rotation and it works on 12 volts too......how economic can you get.
Ian.

PS. I just dug a windscreen wiper motor out of my "goodies" box and as it has the output shaft at 90 deg to the motor body, that would do the trick very nicely.......the motor body is in the vertical mode and the shaft is horizontal which gets it out of the way of the spindle drive belt.

[ihavenofish]

The motor and screw method is perfectly valid. It just has many drawbacks vs the air cylinder ranging from ease of implementation to durability, size, control and cost. Basically worse in every possible way, except the need for a compressor.

[hive8]

I would expect that he is in catch up mode right now, just like any other business after a long holiday. As for communications are you using this address: [email protected]? Skyfire has a nice web site that is still very active.

I'd continue to try to make contact, there is a good possibility that he is simply swamped with work. So far the machine have been well received and as such I can imagine a big demand.

Yes i used both his emails been trying since about 4 - 5 days now. I guess i have to wait a little longer, he is really good with customer service and communication. Hope he is OK.

[johnno402002]

There are a lot of posts here and I have not got through them all. So I apologize if I missed it. But has anybody purchased a mill from Skyfire yet? It looks like his bigger mill in this thread is exactly what I am looking for.

Dan

Hi Dan, I have ordered a SVM-2, the bigger mill. Like you, it is exactly what I'm looking for. It's running late on delivery, Defeng tells me he has lots of orders backed up due to the holidays and high demand. I expected it to run later than advertised as these will be the first to be made by him and I know from experience the first ones have all the unforeseen difficulties.

regards, John

[RichChant]

This has been an interesting read through this thread and I have been exploring different options for a CNC mill, the SVM-0 looks to be what I am looking for although I may save up and get the bigger machine. I would like to know if anyone has received their machine? if so what do they think of the quality? and the big question of how much the shipping from China was to wherever they are. Is anyone able to answer this?

also RE the power drawbar discussion, if you want to go all electric, what about using a 12v metal gear-pump to drive a hydraulic cylinder? those pumps are good for over 100PSI

Thanks,

Rich.