Woodwork related. Forstner bits.

[MattF]

Just asking for future reference incase I decide to do owt like this again. Are Forstner bits usually bad for clogging with MDF, especially once you get past the depth of the cutting head, or is it likely more the cheap bits, (they're the Machine Mart jobbies) I'm using? What other types/style of bit are good choices?

Drilling through a piece of 18mm MDF earlier to make a new screwdriver rack, and I ended up keep stopping the drill to clear the bit out. Roughly three times per hole. As you can guess, when drilling 36 holes, that leads to a bit of a pissy attitude with the drill bits by the time one's finished.

 

[Shedendman]

MDF does that with those bits due to the fibers of the board,what i would do is(if its possible) is to pilot hole all of your holes 1st say with 2mm bit right the way through,then drill with your bits just half way whip it over then drill through the rest,you'll also get a clean hole with no nasty break out.
You dont say what your drilling it with,hand drill or on a press,what speed are you using?

 

[MattF]

Cheers. Wasn't sure if my technique might have been lacking or not. Did it on the pillar drill for a change. Wasn't feeling masochistic enough to do them all with the hand drill last night. RPM wise, can't say exactly, but I'm only running the drill at a few hundred RPM.

 

[slim_boy_fat]

Yes, as said above, MDF will do that. Stalwart's suggestion is what I do, unless of course you're drilling a blind hole, then you're stuck with it.

 

[Parm]

If its just a tool rack your making its quicker to use a spade type drill bitt. Make pilot hole with say a 2 or 3 mm drill bit and then go through with a spade bit. If you clamp a sacrifical backing board to the rear of the panel being drilled it will prevent horrible blow outs. Muck quiker than using forstner bits for this sort of job

 

[clift_d]

MDF can be quite hard going for most cutters. A lot of CNC setups on MDF are apparently set to make several shallower passes at a higher speed rather than one slower deeper pass as it doesn't heat the bits up so much, which in turn can lead to loss of cutting sharpness and burning on your finish. Best thing to try is probably to go at a decent speed, and pull the bit out of the hole several times during drilling to let it clear itself and cool down slightly, which should be easy enough to do on a pillar drill.

 

[BrokenBiker]

I hate using mdf, but when I have to I either use auger bits or spade type bits. don't really use forstner bits for anything except seating hinges on cupboard doors

 

[dan.taylor.1]

Forstner bits clog anyway, you have to peck with them. I'm seconding using a backing board and a spade bit having done it before and had good results.

 

[Wendelspanswick]

You could try Sawtooth Edge Forstner bits:
http://www.ockenden-timber.co.uk/index.php?main_page=product_info&products_id=681
I am a great fan of Forstner bits, ideal for drilling big holes in PVC dado trunking and back boxes without snatching or having to clear the blank out of a hole saw.

 

[printcom]

I find MDF has similar abrasive properties to emery cloth, dulls the edges of most bits very quickly. If you dress up the edges every 3 or 4 holes with a diamond file it keeps them sharp and they don't clog up as much. Personally I don't tend to use forstner bits for through holes, Auger bits are much easier and don't clog up.

 

[MattF]

Cheers for the advice chaps. Looks like I'll be broadening the size of my drill bit selection shortly then. Not oft I tend to drill much in wood these days, above the sizes that a normal drill bit will readily cover, but after the cursing I was doing during that drilling session, I'll be making sure I'm better armed from the advice above for next time I might drill holes above 1/2".

 

[Keith 66]

A lot of the cheaper forstner bits are ground rather badly with a very shallow or flat angle on the bottom of the cutting edge, this means heavy feed pressure is needed before they cut. A touch up with a dremel makes them cut a lot quicker.

 

[MattF]

Cheers. I'll give them a check over and see if I might be able to improve their edge.