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Discussion Starter · #1 ·
Hello.

I just purchased a 4040 CNC machine with a 300w spindle. Because the spindle is low-power, i'm worried about burning the motor out. Say if I wanted to make letters 1cm deep, and 1cm in thickness? Should I remove 1mm per layer? What would my ideal feed rate be with a 1/2 inch diameter V bit, connected to a 1/8 inch er11 shaft?

How deep can I cut without straining the motor?

If your feed rate is too slow, can you damage the motor?

My warranty is only good for 3 months, but i'm going to try and get a year out of this motor, so I don't want to run it at 20000 rpm and burn it out.I want to use softwoods like pine and spruce.
 

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300W is pretty small. Slow feed won't kill your spindle but can cause overheat problems and shorted bit life.

Take some time to understand feeds and speeds. That's an overlooked area for a lot of beginners. Each bit and material has an optimal chip load. Load is based on the number of flutes, spindle speed and feed rate. Too low and you have rubbing and friction. Too high and you stress the motor and/or frame. Plus, you can get a very poor cut and broken bits. Look to the bit manufacturer for feed and speed recommendations.

The thing you will need to figure out on your own is how much of a depth of cut your machine will allow. It has to do with the spindle but also with how rigid your machine is. The cheap Chinese machines are notorious for flexing under load which means poor cut quality. You compensate by using a shallow DOC with multiple passes and thus a much slower process.

I'd start out fairly conservative and then move up. Can you control spindle speed? If you can't get a high feed rate, you can cut your spindle speed. You can also go to a single flute bit which doubles your chip load.

Also, I've never seen a 1/8" shank V Bit with a half inch diameter cutter. Where did you get it?
 

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David - Machinist in wood
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Welcome to the forum! Add your first name to your signature line to clear the N/a in the side panel and so we'll know what to call you. Add your location, as well.

What material are you cutting? If your feed rate is too slow you'll likely burn the wood, or at least get it smoking. And a feed rate too slow will get the bit too hot and that will damage the bit.

Your chips need to carry the heat off the wood and the bit. I cut fairly aggressively and the chips and wood are pretty warm but the bit is no more than every so slightly warm when I finish a cut.

David

Edit - You and I were typing at the same time, Phil :grin:
 

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Welcome to the forum! Add your first name to your signature line to clear the N/a in the side panel and so we'll know what to call you. Add your location, as well.

What material are you cutting? If your feed rate is too slow you'll likely burn the wood, or at least get it smoking. And a feed rate too slow will get the bit too hot and that will damage the bit.

Your chips need to carry the heat off the wood and the bit. I cut fairly aggressively and the chips and wood are pretty warm but the bit is no more than every so slightly warm when I finish a cut.

David

Edit - You and I were typing at the same time, Phil :grin:
I just have my feed rate cranked up higher than yours!
 

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David - Machinist in wood
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I just have my feed rate cranked up higher than yours!
Want to have a spitting contest??? :wink: I cut 1/2" Baltic Birch in one pass at 175 ipm on a regular basis but have cut at 250 ipm a few times and have been told that 175 ipm is very conservative and that I need to be cutting faster. I even cut at 600 ipm once! :grin:

David
 

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David - Machinist in wood
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Haha! Just having phun, Phil. When I go to my friend's cabinet shop where he has his $100k CNC and cutting 3/4" plywood and MDF at 800 to 1200 ipm in one pass it makes my machine look like a toy. LOL! Someone always has one bigger/faster/more powerful whether it's a CNC, table saw, bandsaw, jointer, etc.

David
 

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Discussion Starter · #11 · (Edited)
With my first cut, I did a feed rate of 2mm (0.08 inches) a second, to cut a circle 7cm (2.75) in diameter. My depth of cut was 1mm (0.04 inches) each pass. It sounds like I was way to slow :)

I have manual RPM control... If I had to guess I was around 12000. I just turned the knob, and didn't look at the screen.

Anyways... I'm wondering if you can go fast, as long as your the depth of cut is shallow. For example if I take 0.5 millimeters off (0.02 inches), each pass, can I go really fast?

Does the trade off with a 300 watt motor, mean... I should keep my depth of cuts more shallow than someone with a 1.5 kilowatt machine?

Here's a photo of my machine. I think it's a step above the 3018's you see on Aliexpress.
 

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Generally we talk about feeds in mm/min or in/min (IPM).

You will need to experiment and find where your machine performs well. But, I'm pretty sure you can go faster. On my machine I started at about 500 mm/min and ramped up to 2000 mm/min. For wood, typically, I take a depth of cut around 1/2 the bit width for end mills (straight, spiral, ...). With Ball Nose, pretty much the same. A V Bit is harder to figure out because the deeper you go, the higher the load, even with multiple passes. I typically use a relatively shallow finish cut - .2 to .4 mm. These were all arrived at via experimentation. I kept upping the feed rate until the cut quality degraded and then backed off a bit. I still tweak it based on the material.

As you work with your machine, you will get a better sense of where it's sweet spot is for a given material. There is no substitute for doing.
 

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Discussion Starter · #13 ·
300W is pretty small. Slow feed won't kill your spindle but can cause overheat problems and shorted bit life.

Also, I've never seen a 1/8" shank V Bit with a half inch diameter cutter. Where did you get it?
Forgive me, but i'm Canadian... I just took my digital caliper and got 6mm on the shank, with 22 mm on the cutter. That converts to 1/4 inch on the shank and 7/8 inches on the cutter.

It came with my CNC, and there are no measurements... So I'll have to measure them myself.
 

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Discussion Starter · #14 ·
As you work with your machine, you will get a better sense of where it's sweet spot is for a given material. There is no substitute for doing.
I just don't want to burn out the motor. The guy who sold it for me, works for the factory in China that produces them. He said the motors fail pretty quickly, because of the low power (300 watts)... So my guess is, people don't know how to use them... and they have had to deal with returns

It's the same thing with blenders, you can burn the motor if you use it wrong?

So what can I do... to keep the motor safe from burning out?
 

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You'll just need to use it. If you hear the spindle bogging down, decrease your DOC. If you see poor cut quality, decrease your feed rate. Also, feel the spindle while it's running. If it's getting hot, slow down the feed or decrease the DOC. I have a contactless thermometer that I used when getting to know my machine - it runs totally cool even after an hour of routing.

You might want to consider getting a trim router to replace your spindle. I have a DW611 and it seems to do ok. Haven't had a problem with it yet. I've got several hundred hours on it to date.
 

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Discussion Starter · #17 ·
You'll just need to use it. If you hear the spindle bogging down, decrease your DOC. If you see poor cut quality, decrease your feed rate. Also, feel the spindle while it's running. If it's getting hot, slow down the feed or decrease the DOC. I have a contactless thermometer that I used when getting to know my machine - it runs totally cool even after an hour of routing.

You might want to consider getting a trim router to replace your spindle. I have a DW611 and it seems to do ok. Haven't had a problem with it yet. I've got several hundred hours on it to date.
What's the absolute minimum RPM you would recommend? If the RPM is too slow, can you damage the machine? I'm wondering because I have very narrow bits for high resolute cuts (relief art), and don't wanna break them.
 

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Discussion Starter · #18 ·
I have a contactless thermometer that I used when getting to know my machine - it runs totally cool even after an hour of routing.
You mean one of these things? Just aim it at the Spindle... Thanks for the advice :)

What temperature would be too hot, and what is optimal?
 

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David - Machinist in wood
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As you work with your machine, you will get a better sense of where it's sweet spot is for a given material. There is no substitute for doing.
I agree, Phil. Some of the items I regularly cut, like the Longworth chucks, were cut at 125 ipm and a DOC of about 0.2" per pass when I began. Now I cut them at a still conservative 175 ipm but full DOC for the material, about 0.475" in one pass. Nothing changed on the machine or software, it was just me getting comfortable with higher feed rates and greater depths of cut.

Unless your spindle is getting hot while running and doing that often I doubt it will burn out. As has been said, make sure it is running at a good temp - you should be able to touch it with no problem - and adjust your feed rates to get the best cut. Do some tests and keep cranking the feed rate until your cut quality degrades and then back off. Then do the same with the DOC. You'll arrive at a feed/speed/DOC that works for you, your machine, and the material you're cutting.

David
 

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David - Machinist in wood
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You mean one of these things? Just aim it at the Spindle... Thanks for the advice :)

What temperature would be too hot, and what is optimal?
My infrared model quit working but the last time I checked my spindle was around 100° after cutting for about 20 minutes. I can easily put my hand on the spindle and the bit after cutting. Just a tip - wait until the bit comes to a complete stop before testing the temp with your hand... :wink:

David
 
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