# Working with MDF using a router / cnc - Advice needed please



## rjb (22 May 2007)

I have recently acquired a small cnc router which I am using to cut and shape mdf parts used to make models. I am mainly working with 6mm & 9mm mdf and I am using 6.3mm & 9.5mm straight tct router cutters to cut the mdf to shape and to cut slots and grooves so they can be fitted together.

I have little woodworking experience and no prior cnc experience at all and although I have been reasonably successful using the machine to cut the parts, I have a number of questions and concerns. 

My main concern is that the tct router cutters seem to lose their sharpness very quickly and this is affecting the quality of the work as the cut edges of the mdf become quite ragged and furry and after a while the cutter starts to burn. I was wondering how long the cutters should last, and how to get the best life out of them. i.e. how do I determine the optimum cutter speed and feed rate. (With a handheld router you can feel the resistance as you’re moving the tool, but with the cnc it’s difficult to tell as there’s no feedback). 

Also, is it be best to cut the board in one pass or would it be better to take two or more passes?

Is it worth getting the router cutters re-sharpened or is it best to just buy new ones?

Finally, I heard some time ago that there is a particular type of mdf which is better for machining as it cuts more cleanly i.e. no furry edges. I was wondering if this was the case and if anyone could recommend the best type to use..

Any advice would be very much appreciated, 
Thanks.


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## engineer one (23 May 2007)

hopefully scrit will be along soon, but in principal when machining mdf you will see quite rapid tool deterioration. it will reduce when you use thinner cuts.

if your cn process is inexpensive, what control do you have over the speed of the router bit? basically you should want to get the router bit rotating at optimum speed, as well as the feed speed being compatible.

there are better quality mdf's available and this will change the fact, but you should certainly think about re-sharpening the tools.

have you talked to the tool bit manufacturer to see what they recommend?

paul :wink:


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## jasonB (23 May 2007)

You can buy deep-route MDF but not sure if it comes in the thinner sizes, primerily for routing kitchen doors etc. Failing that MR(moisture Resistant) MDF is much better than cheap contract grade MDF from the sheds.

Solid carbide spiral cutters are the way to go, will give a better finish and last upto 5 times longer, Scrit should be able to advise better.

Jason


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## tnimble (23 May 2007)

Also keep your work area clean of the produced dust and clean your bits witha solvent after routing. This helps a bit in keeping the bits sharp a bit longer. I've heard spraying your bit now and then with a little bit of dry ptfe lubricant, but i've no experience with that. Strait bits can be sharpened more easily than curved/coved/beaded ones and can be done by hand using a fine water or diamond stone to repolish the cutters. For cutting depth use multiple passes. One rule is to cut no more than half the diameter of the bit.


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## rjb (23 May 2007)

Thanks for all the advice so far.

I will try cutting the board in two passes rather than one. I have been running the cutter at around 25,000 rpm with a feed rate of around 10mm /sec. Does that sound ok? The adjustment range on my machine is as follows: Cutter speed 10,000 – 32,000 rpm, Feed rate: 0 – 25mm / sec. I wasn’t sure whether increasing the cutter speed would be a good or a bad thing…

I would like to try the spiral stc cutters, but I can’t find a 9.5mm one with a shank diameter to fit my machine (3/8” or 8mm). I have been getting my cutters from Tool Shop Direct, but they only do the 9.5mm with a ½” shank diameter. Can anyone recommend an alternative supplier? …and also a good re-sharpening service?

Thanks again.


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## tnimble (23 May 2007)

The bit RPM is dependent on the cutter diameter. The larger the bit diameter the lower the speed. Getting a good cut while not having the bit burnt depends on the travel speed of the outside of the bit surface. If its to low the cutter cannot pass through the material effectively. If its the high to much heat will be generated. Due to the heat the metal softens and the bit gets blunt.

Net woodworker has a good article on it

The routing speed should be that the pull on the bit is not to high to allow a strait cut without the bit deflecting or breaking. If the routing speed is to low the routed slot will clog up wirh dust causing heating of the bit and blunting it. I feed by hand so I can't comment on the 10mm/s


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## jasonB (23 May 2007)

For cutters suitable for use with CNC machines try Tipman or Wealden Tool, I tend to use the latter, prices include VAT & Postage which is 99% next day.

Remember any sharpening of cutters will alter their diameter so you will need to adjust your programme to take this into account.

Jason


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## rjb (25 May 2007)

Thanks for all the helpful advice - I feel that I have learned a lot about routing from this and also the websites recommended where I found lots more useful information.

I think my main problem was not realising that the burning and premature cutter deterioration was being caused by the feed rate being too low. I had been slowing the feed rate down further and further in my attempts to prevent this when I should have been speeding it up...

I have now invested in some solid carbide spiral cutters as suggested. I'm running them at the optimum speed (slower than before) and I've increased the feed rate by 2x - 3x ...the machine is now performing better than ever .

Thanks again for all the help, much appreciated!


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## Chris Knight (25 May 2007)

rjb,
You might also try replaceable tip cutters I use KWO and these are very good.


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## jasonB (25 May 2007)

I also use the Versofix and easytip cutters from wealden for general use but the spirals will still give a better finish with the CNC, the cutting angles are much better.

Jason


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