Making Curved Casings from MDF

MDF is rough on knives, which makes custom moulding runs costly. January 12, 2009

I've been hired to produce some interior curved casings. They will be painted and are the Brosco B200 Windsor casing, which has some detail in the profile. I initially thought of making them with pine or poplar, but am now considering using MDF since all the matching straight casings are made of MDF. Has anyone ever made moldings using MDF? If so, what were your results/difficulties?

Forum Responses
(Architectural Woodworking Forum)
From contributor A:
The biggest issue is knife life. MDF is extremely abrasive. But to do a few casings, I would think that M2 steel should hold up for awhile. I'll leave that to someone with more experience running MDF mouldings.

From contributor R:
Carbide, carbide, carbide. Very expensive, high speed steel will melt right in front of your eyes within a hundred feet. You might get away with it if you only have a few feet to do.

From contributor C:
Skip the gymnastics, and use poplar. I sometimes use MDF for arched casings (in the event of defunzalow), and don't have words to express the level of enjoyment I get from it. In actuality, though, there is not that much greater effort involved in strip laminating the radiused casing blank, and then milling it (primarily drying time), and the end result is a better product. This is assuming that you have the tools to produce this quickly (tablesaw with powerfeed, or slr, jointer, large planer).

From contributor D:
Would someone tell me what defunzalow is?

From contributor C:
defunzalow = the funds are low

From contributor L:
Price of carbide knives for a short run job is usually a killer. Don't know your capabilities, but here: SL rip poplar, glue on an adjustable form (if too big for this form, CNC a male/female form), widebelt to thickness, make matching knives on Weinig profile grinder, set up on Stegherr arch molding shaper, touch-up sand, done. An alternative is to program the pattern into the CNC and run in MDF. All depends on quantities and patterns.

From contributor G:
The profile that you mentioned is quite aggressive. I would agree that you'd be lucky to get 100' of MDF with HSS knives on this one. In general, depending on the combination of how aggressive the profile is and the brand of MDF being used, you should be able to get up to 200' of MDF with HSS knives on most profiles. Having said that, the knives will not even be worth re-sharpening after running the MDF. For larger runs you will have to look at carbide.