Feed Rates and cutters for wood panels

I was just about to hit the buy button on a 900x1800 machine when someone questioned the feedrate I should be using on 19mm melamine faced chipboard or melamine faced MDF. I'd mistakenly asked for 2000mm/min or more (based on production time).

The machine is designed for about 3500mm/min. The suggestion was that I should be using 6000 to 10000mm/min.

A quick search on this subject reveals plenty of woodworking forum posts, where whatever speed someone says, someone else always say you need to cut faster eg someone says 15000mm/min and tool lasts 40 sheets, someone else will say "too slow, use 22000mmm/min and tool will last 80sheets" !

Now, I'm not going to be a jobbing shop. The machine will probably be cutting less than 1 hour a week (at 3000mm/min) to make 1 product. And the profit margin on the product would allow for a new £30 cutter every hour. That's being extreme, but I would prefer to spend and extra £10 per job on cutters than an extra say £2000 up front on the machine.

That kind of answers the economics of cutting speed, so next is quality of cut.

I've only manually routed the MFC panels to date, and I get a good enough result with that. The customer doesn't see any edge faces, so I've never though much about the quality of the edge, as long as the melamine doesn't chip I've been happy.

I'm getting a vacumm bed if that's relevant.

I will be cutting a few 6mm wide grooves, some 19mm wide grooves, and then cutting out the profile. So I was thinking to use a 6mm cutter for the lot.

I realise there isn't a question there, just some kind of self justification for buying a machine that feeds at 3500mm/min. I guess I'm hoping someone will say they cut at that kind of speed. And tell me what cutters they use and how fast they wear out.

thoughts?

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(which I think is a problem for a ballscrew machine if I want good precision too).

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Where did you get that information from.
From what I have seen on their website is that they appear to use a lot of supported rails and only a 1.5Kw spindle. I think you need to do some proper research into feed and speeds before buying anything. Are you sure the their machines on designed to run at those speeds or are they just the rapid speeds .. Clive

I just knew I shouldn't have mentioned the machine or ballscrew design. It's removed now.

This thread is part of my research into feed rates.

Everywhere I look I get a different answer, but most of them are 6000mm/min plus.

I want to know if I can get away with 3500mm/min given the cutting does not need to be at the economic sweet spot for tool life or machine productivity.

6mm 2flute down spiral
0.15mm chipload
10k rpm
= 3000mm/min

That might work ?

Hi jimbo,

If 3500mm/min is the max rapids of the machine then I doubt you'll be cutting with any decent DOC at 3m/min. For me that's too close for comfort to the performance headroom. I might be wrong and they can run the machine at 5m/min or whatever and just choose 3.5m/min to be conservative.

I can tell you cutting MDF slowly quickly dulls TCT bits and I wouldn't even bother with HSS as they'll last even less.

I cut around 6-7m/min with 6-9mm DOC in MDF but really depends on your machine. Spindle speed and the number of flutes is important too. If your really going to cut at slow speeds then definitely stick to single flutes. Don't thrash the shit out the spindle either. MDF doesn't need 24k rpm and the slower you go the less rpm you'll ideally use. There's a point where you'll run out of torque on your spindle though so I've found 10-12k rpm is fine for the feeds I mentioned above.

You can get away with cutting at slow speeds such as 2-3m/min but make sure your using the right cutter and keep you spindle speed as low as you can otherwise the cutter rubs rather than cuts and that leads to burning and short tool life.

For wood people think speed is a luxury but having had a machine that cuts at similar rate to what your looking at and now one that cuts it how its supposed to I can tell you its world of difference.

OK thanks.

You are correct, I need single flute to get the chip load OK. They are a bit harder to find and more expensive than 2 flute it looks like.

For 19mm MFC I think I need 22mm or 25mm cutting length? I have seen some 20mm length is that too short?



6mm 1flute down spiral
0.3mm chipload
10k rpm
= 3000mm/min feed
= 3.1 m/s cutter speed

Is that getting better. Now I've lost the cutter speed tables I saw earlier.

If you really are just cutting for an hour every week then the this machine should do you fine. The feedrates of 22m/min in 18mm birch you were quoting are for big industrial routers that have big spindles, servos, vacuum systems and possibly tooling ( You can only push a 6mm cutter so fast) Any small scale machine is not going to match that performance in terms of 1. cut quailty 2. Last any time before something breaks/shifts/loosens/bends.

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Originally Posted by jimbo_cnc

OK thanks.

You are correct, I need single flute to get the chip load OK. They are a bit harder to find and more expensive than 2 flute it looks like.

For 19mm MFC I think I need 22mm or 25mm cutting length? I have seen some 20mm length is that too short?



6mm 1flute down spiral
0.3mm chipload
10k rpm
= 3000mm/min feed
= 3.1 m/s cutter speed

Is that getting better. Now I've lost the cutter speed tables I saw earlier.

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What about a compression cutter to prevent chipping that melamine facing?

Isn't compression cutter just a different name for down spiral?

Compression cutters have both up cut and down cut flute patterns.

Ah right. I see a lot of them have mostly down flute and a small up flute, that explains how I got confused because people were talking about them pushing the work down.

I've cut a few small pieces of MFC on my little 6040 using my standard manual tools, 1/4" with 2 straight flutes. They haven't damaged the melamine edge.

I was hoping to use the same tool for cutting the 19mm edge and for grooves which are about 6mm deep. It looks like I might be lucky and that the melamine will still be on the down flute for grooving.

You can ask 1000 people and they will all tell you a differant feed n speed, WHY.? . . . Because every machine is differant.

No one tell you exact speed N feeds you'll get away with unless they have the exact same machine and even then material and tool grades play some part.
They can only guide you to small degree based on machine spec which is what I did on the phone, the fact you have removed the machine spec makes this harder for folks to help. (And giving attitude when spec is questioned isn't endering)

Now if it was the same you told me with single 32mm ballscrew using steppers then 3500mm/min will be close to rapid speeds which is differant to what you'll get cutting making things worse. Hence why I told you it would be too slow for cutting MFC or MDF and maintain any decent tool life. The spec you told me was IME mixed up and wrong for any decent machine for cutting wood.

By your own searching you can see that average feeds are much higher so what do you want to hear.? . . Best advise in the world isn't worth a cracker if it's ignored, like wise all the sweet words you'd like to hear don't mean a thing if there wrong. They won't make the machine any better suited.!!

As I've said, I'm trying to get away with a slower machine than what is recommended for tool life and productivity. And I'm hoping I can because my requirements are very different to a cnc shop.

And I wanted this thread to be about minimal requirements for a machine, not about any particular machine I'm looking at.

I'd be happy to hear about what machine design WILL fit my needs though, if anyone wants to make suggestions.

I've got another thread about designing a machine, it's still at the stage of choosing steel frame or aluminium extrusion. I got a bit hung up with straightness of rails I think after reading all Sylvaskis epoxy endeavours. So it hasn't got on to drive system yet.

Forgetting about tool life and cut quality for a minute.
3500mm/min is painfully slow, and will get old very quickly. Imo, there's really no excuse for a machine to be designed to have a maximum speed of 3.5m/min.

Now, yes, you can cut at 3m/min with a 2 flute cutter, at 10,000-12,000 rpm, and get good results.

Fwiw, I cut 19mm melamine at about 25m/min every day - on a $100,000 machine.

It was my mistake to originallly say I only needed a slow machine, that's why I was offered 3500mm/min. When I know what speed I need (not what I want!) I can get a faster spec.

OK, here's the machine (1500mm version).
http://www.alibaba.com/product-detai...981060776.html

The advert for the 1500mm bed machine states up to 8000mm/min working speed. Seller has said 6000mm/min is fine, maybe 7000 for my machine. But as Jazz noted, seller has suggested it will mean going up to 32mm ballscrew.

I'm having a 3kW spindle and square rails at the moment.


edit:
I've forgotten one of my principles: always think about resale value. So an abnormally slow machine doesn't make sense there.

So, I will up the speed to 6000 ish. I need to understand the performance disadvantages of 32mm ballscrew, in case seller offers eg only 5000mm/min with 25mm screw, or 6500 with 32mm.

I guess I'm going to have to download octave unless there's an excel spreadsheet calculator around?

I think you might need to ask if it has two screws on the x and what pitch and what is on y and z ..Clive

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Originally Posted by jimbo_cnc

OK, here's the machine (1500mm version).
http://www.alibaba.com/product-detai...981060776.html

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Remember what I said on phone about the Chinese chasing profit which means only one thing, something has to give.!! . . . Look closely at that machine and see if you can spot what is jumping out at me.!! . . (Clue) Sloppy and Baggy needing maintenance ounce a month.!:thumbdown: (No it's not a Women) . . . . And that cost cutting can be seen from out side just imagine what's lurking under those covers and in that control box.??

Don't worry Jazz, I'm having square profiled rails on mine.

Seller will build to what I want, but his opinion is 32mm screw rather than 25mm. He says 10000mm/min will vibrate with 25mm screw. Thisimplies 2510 ballscrew to me. There is no belt on the drive, so that rules out the simple double the pitch and use pulleys to keep the same motor speeds.

He also susgests that 3kW spindle is not powerful enough for 10000mm/min at 19mm depth anyway.

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Originally Posted by jimbo_cnc

Seller will build to what I want, but his opinion is 32mm screw rather than 25mm. He says 10000mm/min will vibrate with 25mm screw. Thisimplies 2510 ballscrew to me.

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Argh Probably because he's got a pile of 32mm screws he wants shut of.!! . . . You won't find many other reputable builders recommending 32mm screws with a single central screw at this width and using steppers.!! . . . . . However You will find many machines this size running 20 and 25mm screws without any trouble.

Also 3Kw will easily push cutter thru MFC at 19mm with correct cutter/size but if your in no rush what does it matter if it's done in 2 passes.? Proper spec'd machine will do 2 passes quicker than one only capable of 3500mm/min.!

By the sounds your sold on the machine anyway, so no point saying anymore really other than good luck.!

Don't be like that Jazz,

I'm here for help to get what I want. Although all I seem to be doing is pissing of all my potential suppliers :)

Those machines you mention are running 2525 or 2020 I assume ?

...and 1 pass at 6000 is quicker than 2 at 10000 :)
Again, this could be my mistake for mentioning cutting at full depth when that might not be an actual requirement.

Your going to need a beefy machine to do 19mm in one pass at 6m. I wouldn't fancy doing that with 6mm tool either! Cut quality would be shite with all the chatter and that's if it didn't snap. 10mm would be where I'd want to be at really.

OK, so that was a bad thing for me to mention as a requirement to the supplier, I'm correcting that now.

I have some 6mm wide grooves, and 19mm wide grooves, both about 6mm deep. I was hoping to cut the whole thing with one cutter but swapping is no biggy either.

What do you recommend if I had 3kW spindle and 6000mm/min ?

The whole job with 6mm cutter and DOC= 6mm?
or 6mm cutter for narrow grooves, 10mm for wide grooves and multi-pass for cutting the profile?

Multipass rough cut the profile, then a full depth finish pass with compression cutter?


I will be hot glue edgebanding the cut edge, and I've got a choice of chipboard or mdf for the core of the melamine board.

If you need both the top and bottom edges clean, then you want to cut the profile with a compression bit.
If you can, I'd try to go up to a 4-5Kw spindle, which should let you cut the profile in one pass with a 10mm compression bit. Machine rigidity will dictate how fast you can go, but I've cut 19mm board in one pass at ~17m/min with a 10mm compression bit.

If your limited to 3Kw, then I'd probably try using a 1/4" compression bit for everything. Cut the profiles slightly oversize in 3 passes, with a final cleanup pass at full depth, removing about .5mm.

Thanks for that.

I'm not limited to anything. I'm just looking for the most economic way to cut 200 boards per year.

The most economical would probably be to pay someone else to cut them.

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Originally Posted by Ger21

The most economical would probably be to pay someone else to cut them.

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It might be close if they were all the same, but say I have 10 model options. That would mean liasing and travelling to the cnc shop everytime someone orders one. That's $50 of my time IF it all goes well, plus the $100 machining fee x 50 visits = $7500 per year.

If I damage a panel later in the build process the costs and delay are horrendous if I can't just run another one off myself.

Obviously there are also many other advantages to having my own machine too, outside of the main 200 board requirement.

Quote:

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Originally Posted by jimbo_cnc

Don't be like that Jazz,

I'm here for help to get what I want. Although all I seem to be doing is pissing of all my potential suppliers :)

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I'm not being or have been anything other than helpful with sound advise.!! You on the other hand appear not to be listening and hell bent on that particular machine so I wished you good luck. Nothing more than that.! . . . . I still wish you good luck.

I'm listening and using the advice I get.

I'm not hell bent on that machine, but no one has suggested any alternative yet. That's not a criticism, just a
fact.

And it appears to meet my needs. Even if it doesn't meet your idea of how fast I should cut wood. (I'm up to about 6000mm/min now, just in case you think I'm still at 3500)

As to ballscrew size, I've asked for 2 proposals from the seller, 25mm ballscrew and 32mm ballscrew, with details of motors and drivers. When I get that info, I will try to analyse the overall performance of the options. Apart from acceleration, what else is there to consider?

as anticipated, next question is acceleration.

I've got some specs:

Motor: 85BHX450B current：4.0A resistance: 0.5Ω, inductance：3.0mH, torque：6 Nm
can't find that on google, but I can just use the values given.

Driver: Leadshine MA860H


I've plugged the values, along with some guesses on gantry weight into the motorcalc spreadsheet, and for 25mm ballscrew it all looks good.

I deconstructed the spreadsheet so I can see the acceleration being used is based on time to achieve feed rate. This results in 0.57g requirement for my cutting.

Is that an appropriate value for this machine?

I'd also like to use this machine for my small plastic parts. I haven't paid any attention to acceleration settings on my 6040, although I might have followed some advice without remembering it. I'm going to run some of my cutting jobs in Mach3 with different motor tuning to see what difference it makes.


32mm ballscrew:
When I plug in the 32mm ballscrew, it's clear the ballscrew dominates. I can get about 0.3g from the motor above. Or I can ask for a larger motor. I was quoted +$100 for 32mm ballscrew, but wasn't given a price for a bigger stepper.

Quote:

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Originally Posted by jimbo_cnc

32mm ballscrew:
When I plug in the 32mm ballscrew, it's clear the ballscrew dominates. I can get about 0.3g from the motor above. Or I can ask for a larger motor. [SIZE=2][COLOR=#000000][FONT=&] I was quoted +$100 for 32mm ballscrew, but wasn't given a price for a bigger stepper.

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It'a not just as simple going Bigger on stepper motor. The drives they are providing now only just about cuts it for that size stepper so going bigger only makes things worse.
It's a Classic mistake often made thinking bigger is better when reality is it's often the worst thing to do. Bigger motors spin slower and require much more power and those drives won't handle larger steppers and give great performance from them.

You Get the performance thru correctly matching screws and motors to rest of machine. Just going LARGE only leads to COSTLY under performing Mistake.!!

Turns out he's not offering a bigger motor, so I have to trade speed for acceleration.

In what aspect is the drive just about cutting it? (for the 25mm design)

Here's an updated calcsheet.
I'm still workig on what an appropriate accelration is to plug in for my two requirements.
Using Mach3, dialling back the acceleration made next to no difference on my plastic parts, but that might be because I cut so slowly in the first place.

If you can achieve .2G, I think you'd be doing very well.
Calculating stepper motors for a target acceleration is very tricky.

Most inexpensive controls use a linear acceleration, meaning you need the same amount of force from start until you're up to speed.
The problem with that, is that steppers lose torque as rpm's increase.
So you have to base your acceleration on the amount of torque your motor will have at your target speed. This may be only 1/4 of the motors rated torque.

As I understand it, I'm below corner speed even at max feedrate, so I have full torque available.

Advantage slow machine! :)

The only time you have "full torque" available is when the motor is not spinning. That's why it's called holding torque. As soon as it starts spinning, the available torque starts decreasing.
If you're spinning so slow that you don't lose much torque, then your resolution is probably poor.

page 3
https://www.geckodrive.com/gecko/ima...cs%20Guide.pdf

Torque doesn't start reducing straight away, it's not until corner speed it falls off.


Resolution is what it is. It's 10mm pitch direct drive and I don't have the option to gear the motor faster on this machine. Driver has serious micro-stepping capability, depending on how you think theoretical resolution translates into real-life accuracy.


When I add power into the calcs, it may reveal some acceleration problems at lower speeds.

Look at a chart from a motor manufacturer. They don't look like the one from Gecko.
Torque starts dropping immediately.

At very low speed the torque is approximately 2/3rds of the rated holding torque. The then gradually lowers from that value then quickly drops off at the corner speed.

The first chart from the first hit on google looks a lot like the gecko chart :)
http://www.orientalmotor.com/product...-only-1-8.html

But I see many different characteristics, so yes, new torque model needed before I look at power and stall.

Yes, 60oz motors have flatter torque curves. But we don't use those. :friendly_wink:

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Originally Posted by Ger21

Yes, 60oz motors have flatter torque curves. But we don't use those. :friendly_wink:

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And if you find a Chinese supplier that gives you an accurate Chart for that particular motor then Frame it because it will be a Rare thing.!!