Word of Caution Buying CNC, from China

**ian** · 4th January 2018, 02:52 PM

question for Elan Jacobs
can Bob's

Originally Posted by Bob Willson

The main rule of thumb that I use is: Only cut to half the depth of the diameter of the router bit and cut at about 1200mm min.
So, a 6mm bit cut at 3mm DOC and 1200mm per min speed at 18000 to 24000 revs per minute

be converted to a material removal rate of around 21,000 cu.mm per minute ?

meaning that a larger bit or deeper cut would require a lower feed rate?
using Bob's example, a 6mm bit cutting 4 mm deep would require a feed rate of around 900 mm/min
while if the depth of cut were only 1.5 mm, the feed rate could be 2400 mm/min

**elanjacobs** · 4th January 2018, 04:27 PM

In essence, yes, but if you go too slowly you'll burn up the cutting edge. The Onsrud catalogue recommends a chip load of 5-7 thou (that's the amount each flute is cutting every time) in hardwood for a 1/4" 2-flute spiral bit at a cutting depth equal to the bit diameter. Feed rate = chip load x flutes x rpm; that works out to 4500-6400mm/min at 18k rpm. Of course, that's assuming power and clamping are no issue.

I never run less than 3000mm/min and that's only with small bits or parts that can break easily, my normal feed rate is 6000mm/min in timber and 12000mm/min for nesting.

My rule of thumb is "Go as fast as possible until the bit breaks, the motor stalls or the finish is unacceptable, then back off a little bit."

**Bob Willson** · 4th January 2018, 04:48 PM

Hi Ian
Not sure of your maths and do not want to go to the trouble of checking it.

However, that sounds quite plausible on the face of it.

Elan
Yes, I could be out by a zero. But I did get it right in the example.

Bugga. Just read the example again and I didn't get it right. Ah well.

**David Mitchell** · 4th January 2018, 09:26 PM

I purchased an ELEKS CNC MILL with LASER Down loaded program (CANDLE) and was unable to get it working ,my son works on computers and he was
unable to get it working
Any ideas would be greatly appreciated
Thanks
Regards
David

**Lappa** · 4th January 2018, 10:12 PM

Might be better to start a new thread.

**woodcncmachine** · 12th June 2018, 08:30 PM

为什么这么复杂？有许多制造商，教程和在线课堂教学。没有多少制造商因为获得了客户的佣金而摧毁自己的声誉。

Mod edit
Google translate

Why is it so complicated? There are many manufacturers, tutorials and online classroom teaching. Not many manufacturers destroy their reputation because they have received commissions from customers.

**reuelt** · 12th June 2018, 11:08 PM

Originally Posted by woodcncmachine

为什么这么复杂？有许多制造商，教程和在线课堂教学。没有多少制造商因为获得了客户的佣金而摧毁自己的声誉。

Mod edit
Google translate

Why is it so complicated? There are many manufacturers, tutorials and online classroom teaching. Not many manufacturers destroy their reputation because they have received commissions from customers.

By supplying pirated & old (2.9) version of Mach3 that works only on Windows XP, many CNC manufacturers in China have ALREADY destroyed their reputation world-wide.

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