Slant bed CNC lathe from scratch

[handlewanker]

Hi, as a matter of interest, the headstock is a design criterior in itself, totally different to normal centre lathe requirements.

A centre lathe is a universal machine in it's material processing needs, which means that apart from four jaw chuck and faceplate work the main feature is the ability to handle lengths of material through the spindle bore, but not necessarily for production requiremnents as in a capstan lathe, but more for longish spindles and drive shafts.

In this mode there is no bar feeder present to steady a long shaft, more often than not there is just a bush or three screws to centralise the shaft at the end of the spindle bore.

Given that you may want to make parts on a repitition basis from bar material, then the bore in the spindle must exceed the largest diam the collets can pass, (32mm) this means the bearings must be large, and if you want to run ally or plastics then 10,000 rpm is not far off the list, and bearings for a spindle with a 6mm wall will need to be about 45mm bore size and be able to handle 10,000 rpm.

You will also need a bar feeder to get the material through the chuck, and this will HAVE to steady the bar as it rotates at 10,000 rpm or the whole machine will go into orbit.

The other side of the coin is if you only want to make parts from precut billets then the bore size becomes irrelevant if at all.

The bearing configuration would be as per normal spindle practice with two angular contacts in "O" configuration at the chuck/collet end and a pair of axially floating radials at the other end.

All of this could be contained in a cast ally headstock housing.

Drive would ideally be three phase VFD with polyvee belt drive to the motor, or direct driven if spindle positioning is a must.
Ian.

[Guldberg]

Casting in alu you say, sound interresting. I have to think about that one, not really sure where to go:-) The main reason for choosing welding is i can have the pieces cut out for me quite cheep and the welding i can do myself. Either way im going to build a mock up of MDF to see if can eliminate some all the design changes that are sure to come when im standing with all the nicely cut steel pieces.

As for the whole headstock thing. I dont think ill need a bar feeder (though it could be fun to make some day:-), the max bore on ER32 collers are 20mm and the bore on 125mm chucks are 30mm. This means i will be aiming for somewhere in between, most likely at either 25mm (1") or at full 30mm. To be realistic i dont think ill ever will be doing production runs in the numbers of 1000's. Just pushing the bar through or using billets will do fine.

Thanks for all the inputs, keep em coming.

BTW i almost recieved all the items listed above, have to take some pictures, they are huge compared to what ive used before

[Guldberg]

Just wanted to show some of the new parts. Im holding the parts to get som sense of size





A bit heavy to hold:-)






This one could almost go as picture taken from an ad

[Guldberg]

I need a little help here, anybody know something about VFD?

I enter a whole new domain of eletronic. I am in the need of a VFD to power a lathe spindle motor. Searching for one on ebay i came across the term "Constant Torque" and "Variable Torque" drives. Apperently variable is for fans etc. where "no load" is provided and constant is for compensation for loss of torque due to lets say a turning operation. So far so good.

My question is, how to tell if a VFD is constant or variable torque? More specifically this is what i have in mind:

http://www.fm.vslib.cz/~kelsub/privr...cument/USS.pdf

I can get the 1.5kw edition for 150$

[Oldmanandhistoy]

My question is, how to tell if a VFD is constant or variable torque? More specifically this is what i have in mind:

http://www.fm.vslib.cz/~kelsub/privr...cument/USS.pdf

I can get the 1.5kw edition for 150$

Link not working for me.

John

[Guldberg]

http://www.fm.vslib.cz/~kelsub/privr...cument/USS.pdf

This should work:-)

[Mike Nash]

The Siemens you linked to is either via a parameter selection. In the case of this particular Siemens it is just changing the V/Hz curve to save a little energy at lower speeds for a fan or pump. There are some models of drives that allow a higher current rated motor to be run when variable torque is selected, but you lose the 150% current limit rating (which you generally wouldn't need for a fan or pump.) This Siemens model still allows the 150% for 60 seconds in either mode. So yes it should work as a lathe drive.

[handlewanker]

Hi Gulberg, I recently bought a VFD, or to be more precise a single phase to three phase converter which does the same thing.

It is 240 volt in with 240 volt 3 phase out and rated up to 3/4 HP, with ramp up and down and dynamic braking as well as a whole lot of other things that you can program into it as needed.

The speed of the motor can be varied by something like 10% of it's rated speed up to 200% by varying the frequency of the waveform.

This has opened up a whole new world of speed control, compared to the previous variable pulley and belt system.

Now I can use all those 3 PH motors that just lie around in scrap yards because nobody wants them and get sold for peanuts as compared to the more popular single phase types.

The problem with single phase types is you can't vary the speed electrically, and I don't care if someone has done it someway, it's not practical.

Apart from the cost of single phase, (anything around 3/4 to 1 HP is megabucks as compared to 3 PH), there is also a physical size to power ratio, and for a similar HP rating the 3 ph motor is more compact.

I bought this unit to control the speed of a bandsaw as opposed to the messy variable belting set-up used on a lot of machines.

Now I'm phasing out (pun intended) all my single phase motors and going 3 Phase.

What I would stress is that the motor is not intended to be run under a load at low revs without some form of cooling, so the mators are chosen to be 3000 rpm types.

Depending on your rev range, the motor is connected by a reduction belt drive to get the minimum rpm rate with the motor still turning fast enough to allow the built in fan to cool it.

On the bandsaw the initial speed reduction is about 1:50 by fixed pulleys, so the range caters for cutting steel and wood by the VFD.
Ian.

[skippy]

Just saw this project and I like it. When I look at the base with it ribs and read the previous comments about straight or diagonal ribbs or casting the whole thing, my immediate thoughts are to go with the straight ribbs (much easier to weld in) and then fill the whole thing with vibrated concrete (or epoxy granite) thus forming the perfect sandwich which would be much stronger than any other design not to mention superior reduction of harmonics. You wouldn't even need a base plate.
I just wish I had a friend working nightshift on a laser and a father-in-law who does coatings.....some people have all the luck....

[Guldberg]

Ive been looking at the epoxy granite thread that's been going on in here. Sounds like a great idea, only problem i see is that this thing is already getting so heavy i will have great trouble moving it around while i work on it. One positive thing could be, that i could downsize the steel to maybe 10-15mm instead of the planned 20mm...wait a second maybe this is a great idea actually:-)

I need some help here, what size power supply will i need for the 2 of these steppers:

Rated voltage: 2.3v
Rated current per phase (amp DC): 5.5

I'm looking at a 42v 24amp transformer, would that be sufficient? That makes 59v after the current has been rectified

[Guldberg]

Look at this beauty:-)

2.2kw/3HP VFD, i think ill have plenty of power to play with. Demo model (never used). Pricetag 220$. I also won an auction on 2 motors 2.2kw and 1.5kw At a total of 40$, lucky me

[Guldberg]

And now we have a motor...



But how do i connect it, help me out here. This is how it looks like in the motors electric box



And this is the VFDs motor terminals



From the cover it looks like i should connect the 6 terminals across 2 a pair:

W1->V2->W/T3
V1->U2->V/T2
U1->W2->U/T1

Have no clue if that is correct?

[ger21]

From the cover it looks like i should connect the 6 terminals across 2 a pair:

W1->V2->W/T3
V1->U2->V/T2
U1->W2->U/T1

Have no clue if that is correct?

You only use 3 of the terminals in the motor, not all 6. But that's as far as I can get you. You either wire it Y (U1, V1, W1 I think) or Delta (U2, V2, W2). Not sure which.

[Guldberg]

Im pretty sure i need the delta, thats for 220v as far as i can tell. What confuses me is that on the lid it looks like when in Y (380v) configuration the 3 upper terminals are connected and when in delta each of the 2x3 terminals are connected in pairs. How very odd:-)

[ger21]

Looking at that again, it looks like the lid is upside down and I had it backwards, and the Y would be the 2 terminals.

[Guldberg]

Aaa, yes, you are right. If you look closely you can see that V2, U2 and W2 are connected across with a small bracket. That must mean that acording to lid the configeration i wrote at first:

W1->V2->W/T3
V1->U2->V/T2
U1->W2->U/T1

must be the correct. Hmm, do i dare:-)

[ger21]

No, you still don't use all 6 terminals. My guess (and just a guess) would be for Delta to use

U1 > U/T1
V1 > V/T2
W1 > W/T3

Send a PM to Al_the_Man and ask him. http://www.cnczone.com/forums/privat...o=newpm&u=2389

[Guldberg]

I followed the command of the lid, all hail the lid... :-)

It ran just perfect. There is a ton of settings in the VFD, but ill figure them out when i tune the motor when the lathe is finished (next year or so:-)

[handlewanker]

Hi, sweet music when you press the button and the motor powers up at your command and is so controllable.

There is nothing on earth that compares to VFD for speed control, and I expect there'll be a whole lot of other solutions but none so simple.

Once you have the VFD in your shop you won't want to even consider single phase anymore, I presume this is single phase to three phase converter and not just a variable speed controller?

Cancel the last statement, the motor you show is 3 phase, so this means you're using single phase in to three phase out.

A unit of 2.2 KW is quite a power pack, watch your fuse boxes, the ability to handle this much power is quite a lot for a domestic supply.

I recently bid on Ebay for a transformer to drop the mains 240volts to 110volts for a tool and cutter grinder I bought from the States, also on Ebay.

The seller stated that it was about 5 amps output, or maybe we were on different wavelengths, whereas it was 5Kva, big difference, I think the primary is about 20 amps, which is far more than enough for the T&C grinder.

So I paid A$25.00 on a "Buy It Now" bid, which was a give away, and local pick up as well.

The only fly in the porridge is when it was connected up it tripped the 15amp mains breaker on switch on.

This is because the transformer is practically a dead short when the power is applied.

When it did connect, once in five tries, and the breaker held, the unit works fine.

So now I'm either going to have to get a large capacitor (? value) across the imputs, or try a large resistor (? value) in series with the input to slow the inrush of current until the voltage has built up and I can bypass the resistor, using a relay.

Any thoughts on this problem would be welcome, as another transformer to give at least 8 amps at 110 volts, which is all I really need, would cost about A$200 plus delivery.

Changing the motor is not an option as it's part of the grinding head.

My own thoughts on the lathe bed build which was indicated at reducing the metal thickness in order to lighten the load and replace the metal with epoxy fill is not a good idea.

My opinion is that the epoxy fill, not being continuous and connected, would only be acting as a resonating damper, and reducing the metal thickness would reduce the torsional strength while gaining very little weight reduction, apart from the fact that the welding will have a reduced strength structure to react on.

Later on, when the project is finished, the weight reduction will not be a factor as a design feature, and cannot be rectified by adding additional metal if at all.

In this design, resonance would not be something to consider, unlike a "C" frame mill design where there is a large overhung leverage to worry about as the head is reacting to the cutter tooth impacts and so resonance is a real pain.

You could always drill a series of 25mm holes in each rib, while INCREASING the thickness of the ribs a bit, and gain additional torsional strength but reducing the weight quite significently by drilling the holes.
Ian.

[Guldberg]

The project continuous, im hunting ebay for all sorts of fun things. I have made a mock up in MDF of some of the construction, based on this i think i will go for 15mm steel, also due to the fact that lasercutting above this thickness apparently requires additional machining.

I desided to make the stand/cabinet for all the electronic etc. first before i start build the lathe itself. Ive ordered the steel tubing (free of charge) and two plates to mount all the electronics on. One for high voltage and one for low voltage.

Anyway, now for some pictures. This is the control consol. Basicly its a 15" LCD touch screen, a silicon keyboard and some buttons for the most commenly used functions and some status led's

Lasercut 3mm steel (10$). The bottom bend a little where the keyboard will go


Backside of the the plate with all the buttons and leds. Soldering is boring in the long run


Back for the consol. LCD mounted partially


LCD, buttons an keyboard mounted




All there is left is to make the arm bracket, bend some sheet metal to cover the back and disassemble it all and send it of to be coated in a nice thin layer of black PTFE