Boring MDF Without Blowout

      Bit speed, bit material and bit geometry could all be factors if MDF blows out as the drill bit exits the material. November 25, 2005

Question
I am in the process of boring 1" MDF through using an 8 mm thru point Amana boring bit. I am having lots of blowout and I need a clean hole. Has anyone found a CNC boring bit that does not blow out the bottom side? The machine is a point to point CNC pods for vacuum. I don't want to use a backer board if at all possible.

Forum Responses
(CNC Forum)
From contributor M:
Most point to points have parameters for drilling speeds that are set for different types of bits. For instance, a through bit would be slow entry into the panel, fast through the heart of the panel and a slow exit. Read the manual and identify the correct terminology for the different types of tools and how to take advantage of them. Most people just tend to skip over that stuff and hit with one speed. Your other choice is just to feed slow through the depth of cut 1000mm per minute or slower if your machine will let you.



From the original questioner:
Thanks for your feedback. I have already thought of that and slowed it down.


From contributor I:
I think the first question should be… Are you using a thru point bit or a brad (dowel) point bit? I have gone through 1" MDF many times in the past and never had any blowout. Sometimes a little chipping around the edges if the lance was getting a little dull, but that was the worst of it.


From contributor J:
Are you using a carbide-tipped or solid carbide bit? A solid carbide bit may be required. We have found that solid carbide bits work better.

An alternative is to first bore the hole as usual, but leave 4-6mm of material. Then bore the same hole again as a through hole. That should greatly reduce the blowout, but it obviously increases the boring time.

We have had similar problems with 1" MDF. We have tried every possible combination of plunge and spindle speed, but to no avail. Our thru-hole plunge works similarly to the way contributor M described.



From contributor I:
We have always used carbide tipped drills. Another option would be to bore from both sides. This would guarantee no blowout, but it will increase your cycle time for each part.


From contributor J:
Perhaps more importantly, there is a big difference in geometry between the solid carbide bits and carbide-tipped bits. At least there was in those that we used.


From the original questioner:
We haven't tried the solid carbide. I need an 8 mm. Where can I get some? I knew you could get smaller bits in a solid carbide, but not larger bits such as 8 mm.


From contributor J:
Courmatt should have them. Did you ever try the solid carbide bits?


From the original questioner:
I have ordered them. I was very pleased with the folks at Courmatt - thanks for referring them to us.

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