Part guide tearout

[pandamonium54]

Using my Parf guide mk2 for the first time. I just drilled the 3mm holes on a 4x8 top, and I’m 50% sure I want this thing to be reversible. So I’m thinking about doing half depth holes with the 20mm bit, flipping it, and doing it from the other side. My question is: has anyone done it this way? Pretty much every video I’ve seen (and the instructions) call for full thickness plunges. I took a closer look at the cutter head. Does it cut through MDF without much tearout?

 

[MikeGE]

When I made my MFT-style workbench, I used Valchromat for the top instead of MDF and used the Parf MK2 for the 200 holes.  There was blowout on about half of the holes on the bottom.  The blowout could have been avoided or reduced had I used inexpensive OSB as a backer board when making the 20mm holes.  Any blowout with using the backer board could have been handled easily with the chamfer cutter.
You might be about to make the 20mm holes half the depth on the first side and then flip the board over for a second pass, but you have to be careful about not going too deep on the first pass.  The pilot point on the 20mm cutter could enlarge the 3mm holes and throw off the jig alignment.

 

[rvieceli]

[member=71822]pandamonium54[/member] The best way to avoid blow out on the back side of the cut is to utilize a sacrificial backer board on the work piece. It needs to be in close contact with the piece you are working on. I used a extra piece of MDF when I did my top. A backer should eliminate most of the tear out.

Ron

 

[pandamonium54]

Thanks for the tips. I didn’t have the foresight to order a thin sheet of MDF for backer board duty, so this thing is being drilled on the 8020 frame it’ll be bolted to. I’ll try doing a shallow set of holes on this side. I have some other UJK accessories that I think will allow me to register off a shallow-ish cut to align the jig on the entire face. I guess worst case, I have a poorly aligned bottom few mils of my holes. Best case is a double-sided MFT.

 

[Crazyraceguy]

I suppose it depends on what you intend to do with the holes. If you are just using them for the through-hole clamps, a slight misalignment will not matter at all. With dogs or the newer lever type clamps, that off-set might matter, because there would be less contact.
I have done this a couple of different ways.
The first time was done with a full-sized template, made by a CNC machine. That one was a full 1 1/8" thick, which brought its own challenges. The clamps won't fit in a top that thick. That meant cutting a huge 45 degree bevel on the underside. Having over 250 holes made that a lot of work.
The second time was with the Parf-guide system. I also had a CXS by that time, which helps a lot.
I have no idea how accurate the first top actually was, since I didn't use it with a guide rail back then. I can however tell you how good the Parf system can be. I have heard of people having issues with it, but taking proper care as you go, should yield great results. Mine is dead-on over the entire 4' x 8' surface. I did drill mine over some scrap, as a backer, but not all at one time. I did it in sections, over a few days.

 

[Vtshopdog]

My parf drilled holes have minimal tear out and once chamfer is cut it’s not an issue.  You do need to use a little care and back off pressure as bit exits the bottom of panel.

My opinion is any issue from tear out will be minimal compared to the likelihood you will have some misalignment boring from both sides plus doubles your work time. My dogs fit super tight on my top and I suspect drilling from both sides would make this worse. 

How about a sheet of foam board insulation and/or painters tape on the backside when drilling?

 

[Crazyraceguy]

Mine are tight too, which I like. I have a hand reamer to clean out the occasional glue spill. This was before the one offered now that is drill operated, plus the chamfer. I need to get one, but the last time i checked, they were out of stock.

 

[Vtshopdog]

Mine are tight too, which I like. I have a hand reamer to clean out the occasional glue spill. This was before the one offered now that is drill operated, plus the chamfer. I need to get one, but the last time i checked, they were out of stock.

I have the drill operated reamer (like it ok) and the hand powered chamfer tool. 
For chamfers, I go find my cordless router and a piloted 45 degree bit unless it’s just a couple holes or I want to get some Popeye the Sailor forearms. Super tight fit and Waaaay too hard to spin that thing….

Is there a combo reamer/chamfer bit now?

 

[Mini Me]

Thanks for the tips. I didn’t have the foresight to order a thin sheet of MDF for backer board duty, so this thing is being drilled on the 8020 frame it’ll be bolted to.

Clamp a backer board to it and if needed a couple of stiffeners from one side to the other. Another way though it would be a bit of mucking around is to partially drill some holes and screw the backer board to the underside of the top. The problem with that is at the end you would need to swap the screws around to finish it off. 

 

[Crazyraceguy]

Is there a combo reamer/chamfer bit now?

Theoretically yes, but they seem to be out of stock.