What Value To Use For Tooth Load?

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Phil
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What Value To Use For Tooth Load?

Post by Phil » Thu 21 Mar , 2013 12:49 pm

The QuickCam Pro help file proposes a formula to calculate feedrate:
Feedrate (mm/min) = Tooth Load (mm) * Number of teeth * Spindle Speed in RPM

Please can anyone explain how to know what value to use for tooth load?

The help file includes a table of suggested tooth loads (for various cutter types) for low carbon steel, brass, aluminium and plastics. However, there is nothing for woods/MDF/Plywood (which is what we use at our school).

Also, wouldn’t tooth load depend on factors other than material and cutter type. We use cutters from 2mm – 12mm. Wouldn’t the tooth load be substantially different between these?

Any help/guidance appreciated.

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Steve
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Re: What Value To Use For Tooth Load?

Post by Steve » Thu 21 Mar , 2013 13:39 pm

Hi,

I would use feeds and speeds similar to those suggested in the VR Milling material library or quickCAM 2D Design.

What material are you cutting and what size of tool?

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Re: What Value To Use For Tooth Load?

Post by Phil » Fri 22 Mar , 2013 10:27 am

Hello Steve, thanks for the response.

Most of our work is with 6-18mm MDF/Plywood (with a little acrylic). We have straight two flute Trend TCT cutters sizes 2mm to 12mm. I have just purchased our first ball nose cutter as we experiment with 3D.

I have made a few successful simple 3D cuts using the Denford suggested feeds and speeds with 12mm & 6mm cutters. I am a little nervous using this one setting with smaller cutters. I have previously broken 2mm cutters using these with QC2D – which I subsequently avoid by setting a step down of 50-75%.

Also, as we progress onto more complicated cuts I am hoping to learn how to better use the CNC machine. After all, we are a school - learning is what we do! From my recent reading I glean that using one speed and feed per material is not optimal. So I was looking at the formulas in the QCPro help file.

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Re: What Value To Use For Tooth Load?

Post by Steve » Fri 22 Mar , 2013 10:58 am

The feeds and speeds should be set more by experience. If you fit material to the machine and run the spindle most of the time at max RPM then use the manual jog and take cuts in the material.

Using the basics of the quickCAM 2D with stepdown as a % of cutter diameter is normally good. With a 2mm cutter 50% or 1mm deep would be the maximum in MDF or harder materials In foam you may be able to go 300% or 400%

Once you have what seems the appropriate depth set set the feed rate to say 2000mm Min if its a harder material and the feed override to 5%. Then start taking a manual cut and increase on the override pot to a point where you feel it is cutting well.

In the control panel it will display the actual feed you are set at taking into account the overide. Record this and use the value in quick CAM PRO. For soft materials set the feed to 5000mm/min and again turn down the override to 5% then increase to a comfortable cut feed.

Phil
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Re: What Value To Use For Tooth Load?

Post by Phil » Fri 22 Mar , 2013 11:09 am

Hello Steve, thanks again for the response.

I will need to digest what you say and experiment with the machine before I respond. Unfortunately, I will not have time before the school easter break so it may be a few weeks before I ask another question resulting from your post.

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Re: What Value To Use For Tooth Load?

Post by Phil » Fri 22 Mar , 2013 11:26 am

Actually, I have an immediate question regarding controlling the step down when using QCPro.

Does setting the step down for a cut impose a maximum step down if Adaptive Step Down is checked?

i.e. When using a 2mm cutter I set step down to 1mm and check Adaptive Step Down. Does this mean the step down will adapt but never exceed 1mm?

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Re: What Value To Use For Tooth Load?

Post by Steve » Fri 22 Mar , 2013 12:13 pm

If you set the stepdown to 12mm the cut will not exceed 12mm in one pass.

If you select addaptive stepdown then the cutter will create multiple passes if the sides are slopeing

See the samples below.

Note if you are carrying out a finishing pass then the software assumes that the model has already been roughed out and goes to full depth from the start.

So if you had roughed the model as shown below with addaptive stepdown off the roughing takes much less time but in places the finishing pass could be removing 12mm of material.

with addaptive stepdown on the finishing pass would be much lighter.
Attachments
adaptive stepdown off (Medium).jpg
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adaptive stepdown off1 (Medium).jpg
adaptive stepdown off1 (Medium).jpg (26.5 KiB) Viewed 4046 times
adaptive stepdown on (Medium).jpg
adaptive stepdown on (Medium).jpg (64.13 KiB) Viewed 4046 times
adaptive stepdown on1 (Medium).jpg
adaptive stepdown on1 (Medium).jpg (26.29 KiB) Viewed 4046 times

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Re: What Value To Use For Tooth Load?

Post by Denford Admin » Fri 22 Mar , 2013 13:37 pm

Phil wrote:Actually, I have an immediate question regarding controlling the step down when using QCPro.

Does setting the step down for a cut impose a maximum step down if Adaptive Step Down is checked?

i.e. When using a 2mm cutter I set step down to 1mm and check Adaptive Step Down. Does this mean the step down will adapt but never exceed 1mm?
I believe that adaptive stepdown should work like that. My understanding is that if there is a surface at 3.35mm (ie between 3mm and 4mm) then it will create a stepdown at 3mm, 3.35 and 4mm if the stepdown is set to 1mm

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