Straight vs Spiral - MDF (Questions)

Hi again!

I’m just doing more experiments on MDF before I go for a real carving job, and I’m just now starting to go back over my models and program finishing passes into them after a sloppy prototype yesterday using a spiral upcut bit.

I’ve done some reading and seen that the general consensus in this debate is that spiral bits are superior in every way apart from price. If this is true, should I be using my straight bits on roughing passes and spirals on finishing passes to make them last a little longer?

Will I see much of any difference when I’m using MDF? If not, should I just use the straight bits all the way on this stock?

Finally, I’m a little unclear on the ability for a straight bit to perform surface plunges and clearing. One website said that there’s a limit to their vertical depth due to a gap at the end of the blade? I’m not seeing that on these 1/8" straights from Inventables, maybe it applies to larger diameters more. I’d like to use them for pocket clearing (and finishing depth passes as well) if possible, but I won’t bother if it’s going to present more parameters to program around…

Any insight greatly appreciated!

I’ve always used straight bits for MDF without any problems. Given the material used to make MDF, I don’t think it matters much.

A spiral bit would be more useful in areas where there’s wood grain where tear out can occur. Also useful if working with a material that has the potential to melt, such as plastic.

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OK I think I’m going to give it a try tomorrow - do you think it will give the same quality of edge if I do a finishing pass with it at a slower feedrate (compared to a spiral)? Sorry for all the questions, I’ve just been learning a lot in the past couple weeks and I really want to make sure I’m doing everything properly.

I get some chatter when I’m cutting circles still - my wheels and belts are set and tensioned correctly and my feedrate never exceeds 3200mm/min @ 16,000 RPM w/ 1/8" & even 1/4" bits. Should I be looking at something specifically to address this? I hate seeing the bit markings on the edges and would like to be able to wipe them off to do minimal sanding afterward.

If I cut a circle, the bit will chatter at the top and bottom as it moves more along the X-axis (side to side)