Does HDF require different circular saw blades and routing bits to cut cleanly?

Question

I've never worked with HDF before and need to do some panel cutting work, corner radiusing and edge profiling, will ordinary woodworking rotary saw teeth & router blades cut HDF leaving fluffy edges and if so how can I avoid this, e.g. different HDF specialist blades/some other finishing method perhaps?

Answer 1

Sheet goods without veneers like HDF and MDF contain a lot of glue. This means you will want to invest in higher quality carbide-tipped tooling. (I'm not even sure I've seen a pure high-speed-steel tool for sale in the usual places, but it is worthwhile stressing that this is a material that will dull HSS tools fast.)

As for straight cuts, any ATB (alternating top bevel) toothed blades will cut cleaner, but will wear out quicker than TCG (triple-chip grind) toothed blades. But we definitely want a tooth that scores and cuts because these materials tend to want to chip. 40-80 tooth blades will be sufficient, with more teeth perhaps giving you a better edge with diminishing results as you get closer to 80.

Any good quality router bit with carbide cutting edges will work fine. A case could be made for triple-flute being better than double-flute, but I've never noticed a difference in most materials (plastics being the exception). Speed-and-feed for router work is the single most important factor for best finish. This is why I'd recommend some practice runs with any new-to-you material.

(This is also a place where you can experiment with climb-cutting, which can sometimes get you a better finish, though at the expense of a tool that tends to feed itself into the work, which ruins that finish by introducing uneven, wavy cuts. Climb cutting should only be attempted on a CNC machine as it can be very dangerous otherwise - the cutter wants to "grab" the timber and throw it out, or you can even break cutters etc.).

This tooling will make a lot of dust, and so care should be taken to not clog up your equipment or your lungs.

Answer 2

First be mindful that HDF, like MDF, is a class of material and not a specification, so the product can and does vary. MDF spans a range of densities and HDF does too, with the top of the first category smoothly seguing into the bottom of the second. In short, some HDF is more like MDF than other examples.

That said, if you adopt any of the numerous standard practice to help achieve clean router results with MDF you'll assuredly get as good or better results in HDF. Of course start with sharp, clean, carbide-tipped or solid-carbide bits, then select an appropriate router speed for the bit type (style and esp. diameter) and and keep careful control over your feed rate.

In addition, when routing conventionally use a second "dust pass" and use climb cutting where applicable and where you're comfortable doing so.

Answer 3

Carbide or diamond cutters are best, but carbide (and probably even diamond cutters) will still generally leave a "fluffy" edge which requires sanding and sealing.

Be aware that even with carbide cutters (I do not have experience of diamond cutters so can't comment on those), your blades will dull very quickly. Where I used to work, we would run 45° chamfers along edges of MDF boards using carbide cutters in a spindle moulder (shaper) and it would only take about 20 boards (so about 50 linear meters) until the blades were noticeably dulled, misshapen and close to needing replacement or re-sharpening.

You may improve the quality of cut by doing a "roughing" pass and a "finishing" pass, if this is possible with the kind of machining you'll be doing. That is, cut/rout/chamfer it slightly oversize in your first pass, and then do a second "finishing" cut where you come in and remove the remaining milimeter or so. This will likely cause more wear on your tools though, since you're effectively running each cut twice.