Should I use a fixed or variable speed spindle? Does it matter?

[johnnyt74]

Hi all,
I'm currently building my first cnc machine. I've absolutely no experience (of cnc - my job is PLC controlled automation).


It all started because my best mate bought me an Arduino for Christmas.


Funnily enough, I'm not going to use the Arduino in the main build - I'm running it from an old PC running LinuxCNC via a parallel port to a break-out board.


Anyways... I started thinking about what I could use the Arduino for and wondered if there would be a benefit to having a variable speed spindle?


I could control the Arduino from a pot on a control panel to alter the speed of the spindle?


I'll mainly be cutting wood (maybe a bit of engraving on aluminium?).


Any benefit to this or would it be a waste of the Arduino?


Thanks :-)

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[JQ_Quint]

I'm not entirely sure what you mean, but if your asking if do you need to be able to vary your spindle speed between cutters then yes absolutely..
Different diameters will require different rpms also different setups maybe also effect rpm (due to vibration )...


Sent from my iPhone using Tapatalk

[wizard]

Hi all,
I'm currently building my first cnc machine. I've absolutely no experience (of cnc - my job is PLC controlled automation).

The concepts are somewhat the same. This especially if you have done any motion control across a PLC.

It all started because my best mate bought me an Arduino for Christmas.


Funnily enough, I'm not going to use the Arduino in the main build - I'm running it from an old PC running LinuxCNC via a parallel port to a break-out board.


Anyways... I started thinking about what I could use the Arduino for and wondered if there would be a benefit to having a variable speed spindle?

Get a real spindle and a factory made VFD. Seriously! That is a spindle that has an AC induction motor as opposed to a router of some sort.

As to the benefit form a variable speed spindle it to some extent depends upon what you expect to do with your machine. However you really need variable speed if you expect to do a wide range of work on the machine. The optimal spindle speed varies with materials being cut, surface finish quality, type of cutter & etc.

I could control the Arduino from a pot on a control panel to alter the speed of the spindle?

Most VFD's would allow speed adjustment with a pot connected directly

I'll mainly be cutting wood (maybe a bit of engraving on aluminium?).


Any benefit to this or would it be a waste of the Arduino?


Thanks :-)

Good motor control, especially in a demanding application requires a well engineered drive. You can of course spend months or maybe years programming an Arduino to control a motor and building the electronic hardware, but I'm going to say that it isn't worth it. I would highly recommend a proper motor controller and spindle combo.

[johnnyt74]

JQ, Wizard,
Thank you both for your great posts.

Wizard, I was planning on getting a decent (within my budget) water-cooled spindle. I'll certainly look into a combo that allows proper speed control now. Thanks again for the great advice :-)

[plcamp]

That would be a big YES to spindle speed control. Buy what you can afford, but if you look at your future needs, spending a little more now may be well worth the extra expense.

[johnnyt74]

That would be a big YES to spindle speed control. Buy what you can afford, but if you look at your future needs, spending a little more now may be well worth the extra expense.

Thanks for the advice plcamp. Duly noted mate. I think I'm going to go for a variable speed spindle after all that I've read (and to your point about future needs).

Cheers :-)

[ger21]

Any water cooled spindle will be controlled by a VFD, which automatically makes it variable speed.

[johnnyt74]

Any water cooled spindle will be controlled by a VFD, which automatically makes it variable speed.

Great to know Gerry. I'm definitely going water-cooled so should be sorted. Thanks mate :-)

[wizard]

Thanks for the advice plcamp. Duly noted mate. I think I'm going to go for a variable speed spindle after all that I've read (and to your point about future needs).

Cheers :-)

Variable speed is a valuable feature in wood and metal working equipment, i wish I had such for my drill press and a number of other tools I have.

In any event when looking for a spindle water cooling is a good thing. The vast majority of Chinese spindle assemblies are three phase power thus you have little choice but to by a VFD to control it. In any event I get the sense that you aren't up to speed on controls for machine tools. If so I suggest a bit of reading and thread viewing here to get a better idea of what goes into the machine. Control systems aren't especially difficult but they are something that takes an investment in time to come to grips.

[johnnyt74]

In any event I get the sense that you aren't up to speed on controls for machine tools..

Yep, there's nothing wrong with your senses!!

I do work in a factory and program PLCs for a living so I'm knowledgeable enough about inverters / 3-phase supplies etc. But I've absolutely zero experience of machining, CNC, spindle speeds, cut depths/angles, filleting - etc etc.... and lots of other things I've been reading over in the last week or two.

I'm ordering the ball screws for the machine this morning. I've got all the motors on a bench running.

I've got a very good friend of mine (who happens to be a mechanical genius) machining the frame for me (basically chopping down the extruded ally and making sure it fits together).

I've probably got at least another 6 weeks before I have anything that looks like a machine built and intend to spend that time immersed in it the CNC world to learn all I can.

I read loads about different ball screws yesterday (rolled, ground, different pitches, C0 - C7 etc) and intend to do the same for every component. It's a steep learning curve but, so far, I'm really enjoying it.

And thanks to people like you who have all this knowledge, got the T-shirt, and are happy to pass on great advice, it's going to make the journey much more enjoyable! :-)

[A_Camera]

Variable speed is a valuable feature in wood and metal working equipment,

...and plastic as well. I think it is not just a valuable feature but a big MUST HAVE. Before upgrading my spindle I used a DC motor, which I almost all the used at max RPM (~9000RPM) but now I use everything between 6k to 24k RPM and the results are much better.

i wish I had such for my drill press and a number of other tools I have.

Yes, on a drill press it is a real blessing. I have one with a dial, easy to adjust to the material and the drill diameter so of course, it is frequently used and today I can't imagine how could I be without that before.

I also wish my angle grinder and circular saw had a speed dial... many time it would be pretty useful as well IMHO.

[wizard]

Yep, there's nothing wrong with your senses!!

I do work in a factory and program PLCs for a living so I'm knowledgeable enough about inverters / 3-phase supplies etc. But I've absolutely zero experience of machining, CNC, spindle speeds, cut depths/angles, filleting - etc etc.... and lots of other things I've been reading over in the last week or two.

Machining technology is fairly easy to understand but there is a lot to learn. The thing with CNC is that if you get something grossly wrong you will damage or even break tools or overload the spindle. I would imagine you have access to some manual machining equipment, a lathe and a mill most likely to maintain your machinery. There is a bit that can be learned from manual machine tools, just realize that there is much that you might do manually that you wouldn't with a CNC. One thing I often suggest is taking up a machining technology course that a local college might have.

Working with PLC's is fairly straight forward skills transfer to CNC. I work in factory automation so I'm very familiar with the tech. In many cases what is done in automation is exactly the same as what is done in CNC controls.

I'm ordering the ball screws for the machine this morning. I've got all the motors on a bench running.

I've got a very good friend of mine (who happens to be a mechanical genius) machining the frame for me (basically chopping down the extruded ally and making sure it fits together).

Nice!

I've probably got at least another 6 weeks before I have anything that looks like a machine built and intend to spend that time immersed in it the CNC world to learn all I can.

Just don't immerse yourself in coolant. Sorry it has been a long week and couldn't resist.

I read loads about different ball screws yesterday (rolled, ground, different pitches, C0 - C7 etc) and intend to do the same for every component. It's a steep learning curve but, so far, I'm really enjoying it.

And thanks to people like you who have all this knowledge, got the T-shirt, and are happy to pass on great advice, it's going to make the journey much more enjoyable! :-)

Do take your time, you don't want to burn out on this.

[wizard]

...and plastic as well. I think it is not just a valuable feature but a big MUST HAVE. Before upgrading my spindle I used a DC motor, which I almost all the used at max RPM (~9000RPM) but now I use everything between 6k to 24k RPM and the results are much better.

For somebody new to machining I could imagine spindle speeds and feeds being a bit of a mystery

Yes, on a drill press it is a real blessing. I have one with a dial, easy to adjust to the material and the drill diameter so of course, it is frequently used and today I can't imagine how could I be without that before.

I'm not so lucky currently have a Grizzly drill press that I'm not really impressed with at all. for metal working you often want very slow spindle speed sand most drill presses simply don't support properly low speeds. If you try to run a large hole saw through a paces of metal plate you will have issue as the rims speed can be way to fast.

I also wish my angle grinder and circular saw had a speed dial... many time it would be pretty useful as well IMHO.

One tool I have an eye on building (actually have an eye on many tools) is a square wheel grinder, I'd love to make it variable speed right from the start. Almost any machining operation can benefit from support for variable speed. It is just a matter of affording the hardware to do it. On a CNC I rate variable speed right up there with an automatic tool changer.

[johnnyt74]

One thing I often suggest is taking up a machining technology course that a local college might have.

Do take your time, you don't want to burn out on this.

Great advice there Wizard. Especially that last bit. I have to admit I've had a few sleepless nights with every part of the build, software, preparing the space for the machine etc all going around in my head.

I've ordered my linear rails from one of the Chinese sellers on eBay with a month or just over delivery time so, in a strange way, that's helped as it's let me take the "foot off the gas" a bit.

My youngest daughter is round later and she knows all things "college" so I'll enquire as to whether she knows if our college do any kind of night-course or similar.

Thanks again for your help mate :-)

[johnnyt74]

Yes, on a drill press it is a real blessing. I have one with a dial, easy to adjust to the material and the drill diameter so of course, it is frequently used and today I can't imagine how could I be without that before.

Not thought about plastic but definitely going this route. Thanks for passing on your experience. I'll be looking into *which* spindle to get a bit further into the build but I'm definitely going down the variable speed route now :-)

[A_Camera]

For somebody new to machining I could imagine spindle speeds and feeds being a bit of a mystery

Yes, but the mystery is easily understood after the first start... I mean, when you see the plastic or aluminum melting you know something is wrong. If you think about ordinary household experiences then cutting butter with the same knife goes faster than cutting carrot. It requires also more force. I think the same way when using a CNC or drilling with a machine. But of course, to calculate the exact speeds and feeds needed is a bit more complex, that's where FSwizzard, or other calculators help out, at least until one has enough experience and remembers from previous experience what and how to set it up.

I'm not so lucky currently have a Grizzly drill press that I'm not really impressed with at all. for metal working you often want very slow spindle speed sand most drill presses simply don't support properly low speeds. If you try to run a large hole saw through a paces of metal plate you will have issue as the rims speed can be way to fast.

Mine is just a small Bosch PBD40, but while it may look like a toy, it handles everything very well so far. I use it mainly for aluminum and have not having any problems with pretty large holes, the largest I cut so far was 70mm in 15mm thick aluminum. Of course, it is at very low rpm, lubricated, but it is very efficient. Steel and cast iron also works well, but have not drilled anything larger than 13mm diameter in 5-8mm thick material. I am not impressed with the chuck but for some reason I can't seem to be able to remove and replace it. It does not have a locking screw and should be just twisted anti-clockwise according to Bosch, but it does not seem to go. Don't know why.

One tool I have an eye on building (actually have an eye on many tools) is a square wheel grinder, I'd love to make it variable speed right from the start. Almost any machining operation can benefit from support for variable speed. It is just a matter of affording the hardware to do it. On a CNC I rate variable speed right up there with an automatic tool changer.

Yes, on a CNC it is a must. Unless you have a too weak motor, in which case everything is milled at maximum rpm. A tool changer if nice, but not on my list.

[wizard]

Yes, but the mystery is easily understood after the first start... I mean, when you see the plastic or aluminum melting you know something is wrong.

Sometimes learning the hard way is quick. I remember the first time I tried to drill a hole in stainless steel. It is amazing how quickly a drill bit can become red hot!

If you think about ordinary household experiences then cutting butter with the same knife goes faster than cutting carrot. It requires also more force. I think the same way when using a CNC or drilling with a machine. But of course, to calculate the exact speeds and feeds needed is a bit more complex, that's where FSwizzard, or other calculators help out, at least until one has enough experience and remembers from previous experience what and how to set it up.

There are actually many ways to come up to speed. I mentioned the machining courses because many people seem to do better in a class room setting. Unfortunately I was never good at being a student in high school but for some reason I'm a better student in old age.

Mine is just a small Bosch PBD40, but while it may look like a toy, it handles everything very well so far. I use it mainly for aluminum and have not having any problems with pretty large holes, the largest I cut so far was 70mm in 15mm thick aluminum. Of course, it is at very low rpm, lubricated, but it is very efficient. Steel and cast iron also works well, but have not drilled anything larger than 13mm diameter in 5-8mm thick material. I am not impressed with the chuck but for some reason I can't seem to be able to remove and replace it. It does not have a locking screw and should be just twisted anti-clockwise according to Bosch, but it does not seem to go. Don't know why.

Sounds like a left handed screw as is commonly seen in hand drills. Such screws are notorious with respect to the difficulty of removal.

Yes, on a CNC it is a must. Unless you have a too weak motor, in which case everything is milled at maximum rpm. A tool changer if nice, but not on my list.