Mold making in MDF

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Mold making in MDF

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alex bergner	alex bergner posted 5 Years Ago HOT Topic Details
Group: Forum Members Posts: 2, Visits: 26	Hi there, since I am new in that forum, I thought I would share some of the experiences I gained in creating MDF molds as a start (as well as the bladder welding machine in the tools section). As a disclaimer I have to say that I only built 2 frames using this method, so there is still a lot to learn. The reason I am doing MDF molds is that it is cheap and quick. Up to now, I did not optimize for surface quality but for getting my projects done. It takes about 2 evenings in my workshop to create a mold for the tubes of a bike (unless it is as large as the Lotus, then it takes 4 evenings.) So the process is as follows (assuming you built or own a CNC mill which fits the mold): I screw the number of MDF boards on the CNC mill base as needed. For a typical bike frame, 2 MDF boards are sufficient as the resulting mold has 38mm thickness. Adding one board more to increase stiffness seems a good idea in general though. It is important to use a sufficient number of screws to ensure the boards are well bolted down. It is equally important to place the screws in locations which will not be milled later - otherwise the lifetime of your milling bits decreases radically. Sometimes it makes sense to create a milling process which just engraves the outlines of the cavities on the topmost board so you can place the screws right. Then I mill the mold in a roughing fashion. I leave 0.3mm stock. I choose the mill and stepping to have cusps of less than 0.5mm. This is actually quite rough and permits quick milling. A typical setting is 1.4mm stepover with a 6mm ball mill. I also mill alignment holes into the molds (of course) When this is done, I use epoxy to soak the MDF. I do not remove the mold from the mill so I don't have to worry about the accuracy when placing it again into the mill. In order for the epoxy to soak in really deep, I heat the MDF with a heat gun locally really hot - definitely use full protection (breathing mask, ventilation on...) in that process because the epoxy only enters the wood deeply when it is quite hot. As I operate at high temperatures it happens sometimes that I overheat the epoxy and it starts emitting smoke. That's hard to avoid. As I said, use full chemical protection and ensure good ventilation. When done right, the epoxy soaks to a depth about 2-4mm into the MDF, effectively making it plastic-like for further processing. The next day I do the finishing. Usually I mill with a parallel and contour operation with 0.8mm stepover/stepdown on a 6mm ball nose mill. I found this is the best compromise between milling time and sanding time later. Sanding with 180-240-400-800 grit paper finishes the mold. I hope that helps some of you. here are some pictures: Build thread Lotus 108 (in German though) Presentation of the Lotus 108 build
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Lester Populaire	L Lester Populaire posted 5 Years Ago HOT Post Details
L Group: Forum Members Posts: 311, Visits: 13K	+x alex bergner - 10/6/2019 9:09:50 PM Hi there, since I am new in that forum, I thought I would share some of the experiences I gained in creating MDF molds as a start (as well as the bladder welding machine in the tools section). As a disclaimer I have to say that I only built 2 frames using this method, so there is still a lot to learn. The reason I am doing MDF molds is that it is cheap and quick. Up to now, I did not optimize for surface quality but for getting my projects done. It takes about 2 evenings in my workshop to create a mold for the tubes of a bike (unless it is as large as the Lotus, then it takes 4 evenings.) So the process is as follows (assuming you built or own a CNC mill which fits the mold): I screw the number of MDF boards on the CNC mill base as needed. For a typical bike frame, 2 MDF boards are sufficient as the resulting mold has 38mm thickness. Adding one board more to increase stiffness seems a good idea in general though. It is important to use a sufficient number of screws to ensure the boards are well bolted down. It is equally important to place the screws in locations which will not be milled later - otherwise the lifetime of your milling bits decreases radically. Sometimes it makes sense to create a milling process which just engraves the outlines of the cavities on the topmost board so you can place the screws right. Then I mill the mold in a roughing fashion. I leave 0.3mm stock. I choose the mill and stepping to have cusps of less than 0.5mm. This is actually quite rough and permits quick milling. A typical setting is 1.4mm stepover with a 6mm ball mill. I also mill alignment holes into the molds (of course) When this is done, I use epoxy to soak the MDF. I do not remove the mold from the mill so I don't have to worry about the accuracy when placing it again into the mill. In order for the epoxy to soak in really deep, I heat the MDF with a heat gun locally really hot - definitely use full protection (breathing mask, ventilation on...) in that process because the epoxy only enters the wood deeply when it is quite hot. As I operate at high temperatures it happens sometimes that I overheat the epoxy and it starts emitting smoke. That's hard to avoid. As I said, use full chemical protection and ensure good ventilation. When done right, the epoxy soaks to a depth about 2-4mm into the MDF, effectively making it plastic-like for further processing. The next day I do the finishing. Usually I mill with a parallel and contour operation with 0.8mm stepover/stepdown on a 6mm ball nose mill. I found this is the best compromise between milling time and sanding time later. Sanding with 180-240-400-800 grit paper finishes the mold. I hope that helps some of you. here are some pictures: Build thread Lotus 108 (in German though) Presentation of the Lotus 108 build Congratulations the final result looks good! Even tho the porosity would have me worried for the long term behavior. Especially with the diy fork. I am about to finish my first frame. The tubes are made in vacuum infusion on 3D printed mandrels. Then a tube to tube construction from there. For my next frame I'm planning on machining moulds. A first trial with bladder inflation moulding with prepregs in machined and sealed plywood turned out surprisingly promising. Altough this needs more tests before i feel confident enough making a bike frame mould...
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