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Tips for Cutting MDF

Discussion in 'General Phlatprinter 3 Chat' started by Flashsolutions, Jul 5, 2012.

  1. Flashsolutions

    Flashsolutions Active Member

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    I have had my modified Phlatprinter III for quite some time now and in addition to cutting foam, I use the Phatprinter quite a bit to cut 1/4" MDF. I don't recommend cutting MDF unless you have a laminate router mod of some kind on your Phlatprinter III.

    First and foremost, cutting MDF means your X an Y settings must be far more accurate than if you are just cutting foam. You need to be able to cut a rectangle object oriented in the horizontal as well as vertical plane of the material and have them mirror one another when placed one on top the other after being cut out.

    I use a sheet of sacrificial 3mm Depron as a carrier for my MDF sheets which I have cut to 24"x24" squares. Do not use FFF! FFF is too wavy. 3mm Depron provides a consistent thickness and good adhesion to the sand paper rollers. It tracks true and eliminates skewing problems sometimes associated with FFF.

    I have found that a feed rate of 35 IPM with my Bosch Pony router variable speed set to the number 5 on the dial produces the best cuts when coupled with the multi-pass option set to a depth of .05". I broke an $18 bit by trying to push 40IPM with a depth of .08 so keep this in mind if you are thinking of pushing the limits.

    When calibrating, rough in the calibration and then gradually fine tune first the Y axis, getting it to cut a 7" x 2" strip exactly 7" in length before attempting to calibrate the X axis. The Y axis will be your reference as it does not factor in any roller slippage. Once I get close to the 7", I start manually changing the steps per inch using whole numbers. Forget trying to use the auto calibration settings which produce steps in fractions of a whole number such as 527.564824697. Manually setting whole number actually produces better accuracy over the long run. After setting up a whole number, I then make a sample cut in MDF and measure the result, bumping the steps per inch by 1 count at a time till I get a perfect 7". You might need to go a half step forward or back once you get very close. Example, my Y axis is 529.5 steps per inch.

    Once you have the Y axis set properly, repeat with a 7"x2" strip laid along the X axis. When you can cut out both pieces and have them mirror one another precisely, then you are ready to set up tabs and slots for a final check. Put a tab along the long side and a slot in the middle of each piece. Orient these on the same sheet, one in the horizontal and one in the vertical plane. Cut them out and verify they line up precisely. It will probably be difficult to insert the tabs into the slots because, unlike foam, there is little or no compression of the material.

    To make your tabs and slots fit better, we can do a little trick in sketchup. Erase all of your cut lines. Change the bit diameter to be slightly smaller than the actual bit diameter you are cutting with. For example, if your actual bit is .062 (~1/16"), change the bit diameter in sketchup to read .0585 and then reapply your inside and outside cut lines and render a new CNC file. Cut the project pieces with this setting and you will find the tabs and slots now fit a bit looser and don't require a rubber mallet to get them to go in place.

    In case you are wondering what bit I use, I like this one from BitsBits.com [Deep Cut Flat End Mill - 1/8 x 2 - .062 (11.4mm cut length) (DP062F) ] It sells for $18 plus shipping, so I order at least 2 since shipping is $8.50.

    Cutting MDF generates a lot of dust, but the 1/16" bit keeps most of collected within the cut lines. Simply vacumn it out when finished.

    One more thing... tab depths. I set my tab depth factor to 75, my material depth to .025 and overcut to 110%. You don't need many tabs, just two per part is sufficient. I use a Dremel stylus with a diamond cutting disc to cut the tabs free.

    Hopefully, these tips may help any of you who wish to push your Phlatprinters limits.
     
  2. TigerPilot

    TigerPilot Well-Known Member

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    Nice write-up, Flashsolutions. I've been cutting wood on my PP III too. The last time I cut wood it was 3/4" bass wood. It was a big part, 46" long triangle with cuts inside too. Took about 7hr (or was it ten? :p ) to cut one part, and I had to cut two of them. I too use a 1/6" bit, at about $2 each shipped, feed rate 20ipm and multipass set to the default 0.0313. As a carrier I use the dollar-tree foam. I too broke some bits but the pain is waaayyy less at that price. :D :D

    I'll try the two 7"x2" thingy to see how accurate I have my printer set up. I had set my x axis using 8' foam. I used the automatic setup and had made a 7.5' run to calibrate the axis measuring with a measuring tape. I figured that a 1/32" mistake over that length is about 3 ten-thou or so on one inch, totally acceptable for my cuts.
     
  3. Flashsolutions

    Flashsolutions Active Member

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    Your method may even be more accurate than mine if you use a full 8' for calibration. Since I was moving MDF which is pretty heavy and I only use 2' squares for most of my projects, I suspect if you can get consistent readings over 8', you will get even tighter accuracy than I achieved.

    Tell me where you got your $2 bits. I have quite an assortment of less expensive bits that size, but the cutting area is barely a quarter inch long, so these $18 bits provide about .4" of cutting area which gives me a little more elbow room when cutting various materials.


     
  4. jonquinn

    jonquinn Member

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    I cut the router templates I had asked for some help with way back, about 2 months ago on my phlatprinter3. I ran it first on some FFF to make sure it ran OK, then ran the machine with the 1/4" sheet of MDF (24"x48"). I started with the 1/8" bit supplied with the machine, but it broke (too deep of a cut).
    A quick dash to home depot to pick up some rotozip cutters (like a upcut router bit) and I was back in business. I think I had the machine take 0.010"? deep cuts per pass. I just ran the MDF sheet through on its own, but I did have some roller supports on the infeed ad outside side. This was all with the supplied motor tool attachment too, I didn't have time to get the bosch colt attachment ready, plus I was short some hardware too.
    The machine cut perfectly. I couldn't have been any happier with the results. It did take a little time this way (about 1.75 hours), but I came up with a perfect set of templates. The arc was smooth and perfect, and the machine indexed exact every time around, on the many passes it took to cut through the sheet.
     
  5. TigerPilot

    TigerPilot Well-Known Member

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    Flashsolutions, I had posted in the past about the bits I use. I'll see if I can come up with the links again. When I cut the 3/4" bass wood I do not use the 1/16" bit, it's flute is too short. I have a 2.2mm, or so, bit that has a flue of 22mm. For 1/4" MDF I use the 1/16" bit. It's flute length is over a 1/4".

    EDIT: These are the 1/16" bits. They used to be $12 then $14 and now they are $18. Plus shipping, of course. http://www.ebay.com/itm/10-1-16-0625-DI ... 589351132c
    These are the bits I use for the 3/4" Bass wood. http://www.ebay.com/itm/10-pcs-single-f ... 2a1d1da2aa
     
  6. checkers

    checkers New Member

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    I am thinking about adding a Pony to cut various kinds of wood, but I want to use something larger than a 1/8" bit.

    Do any of you have experience with a 1/4" router bit?
     
  7. Flashsolutions

    Flashsolutions Active Member

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    Yes, I have used a number of1/4" bits to cut various types of wood. I should point out that I upgraded my X stepper motor to a larger size than comes with the stock Phlatprinter.

    I have had no trouble cutting wood product including oak. You just have to establish a feed rate and plunge depth that works for the wood you are wanting to cut.

    Again, anytime you are cutting wood, you should use a carrier under it and the carrier should be a consistent thickness if you want to ensure accurate cuts. I have only cut up to 3/4" thickness. The roller tension increases as you increase depth, so keep that in mind.


     
  8. ToxicToast

    ToxicToast Down in the weeds. Staff Member

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    That is really good info, Flash. I still have a stock spindle on mine and it cuts 1/8th inch MDF very cleanly in 3 passes with the 1/16th chipbreaker. But, it is also not as accurate as I'd like-close enough for my onsey-twosey cuts, but not sufficient for production. I also use a sacrifice sheet of blue foam as a carrier and that has never been an issue. However, I'd really like to upgrade to a different spindle at some point to get the speeds and backlash under more control.

    Great info, and I'm probably going to reference this some time in the future when I get around to the upgrade. Thanks!
     

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