deep mortises with drill press? - Woodworking Talk - Woodworkers Forum
 
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post #1 of 17 Old 10-31-2017, 12:39 PM Thread Starter
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deep mortises with drill press?

I need to make six keyed mortise and tenon joints through 3.5 inch thick oak. The width and height are TBD, but somewhere around 2.5 x 1 inches. Similar to the attached photo.

Due to the significant depth, I'm thinking I'll use the drill press to hog out the holes and then flatten the cheeks using a chisel.

My questions are:

1. Is there a particular hole pattern to use, or doesn't it matter? Do forstner bits wander when the holes overlap?

2. Is there a particular type of chisel to use for trimming the cheeks and corners (of the mortises)? Currently I just have a set of generic store-brand utility chisels (read "low quality"), and a single high-quality mortise chisel which is only 1/4 inch wide. I plan to buy whatever is appropriate for this project, but am not sure what that would be. Wide? Narrow? At a certain angle?
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Last edited by desertsp; 10-31-2017 at 12:56 PM.
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post #2 of 17 Old 10-31-2017, 02:14 PM
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There won't be very much deflection with a forstner bit. Where you might get in trouble is having the table perfectly square with with the bit. You might drill half way through from each side. I don't think a forstner bit has enough reach to drill. If anything is off it would be better in the middle of the timber than the other side anyway. If you were doing this a lot you might get a mortising chisel. It has a longer length than a carpenters chisel. A carpenters chisel will get the job done.
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post #3 of 17 Old 10-31-2017, 02:29 PM
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Using your picture above as your guide, mark the vertical of your trestle inside and outside with a pencil.
The outside is the side which will be most visible so this should be the best side.
Scribe the walls for the tenon on the best side. Using your chisel, outline the tenon rectangle prior to starting your drilling. Drill inside your lines from this side.

If you don't have time to do it right the first time, when will you have time to do it over?
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post #4 of 17 Old 10-31-2017, 03:01 PM
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I like my hand tools, so I'll offer this - make sure your stock is nice and square. Market the mortise on both sides of the piece. Drill part way through with any bit that'll go half way through - I'd use an auger bit in a brace because it's long and easy to keep square by eye. Or I'd use a bard point, or an auger bit in a drill. I'd worry about it a forstner bit wandering too and you really don't need a flat bottomed hole, so there's no need for the forster.

If it's a 1" mortise I'd use a 3/4" or 7/8" bit. Drill halfway through from both sides, being sure not to hit your layout lines with the bit. Then chisel to your lines from either side with a 1" wide bench chisel (if your mortise is 1"wide). Only chisel halfway down then chisel from the other side. Keep the walls of the mortise square or angle to the chisel just a couple degree inward to keep from having a hump in the middle of the mortise.
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post #5 of 17 Old 10-31-2017, 03:08 PM
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or you could do what I do and just cheat.

I have a cheap (HF) X-Y vice aka cross slide that I bolt to the drill press table + end mills.
in this case extra long end mills like
https://www.the-carbide-end-mill-sto...ongLength.html

an X-Y vice is the kitty's meow when it comes to making clean slots - very handy if you're prone to making homespun jigs and fixtures that need to be 'adjustable'

make sure your drill press has the required depth travel.
a shallow cut depth per pass goes smooth & quick; taking to heavy a cut is not recommended _especially_ using long mills - they bend, and they snap, and you can get bashed . . . .

it's tricky getting smooth sides by trimming cuts - a mill diameter the full width of course is neat - but gets pricey.
small diameter makes for double number of passes - a diameter well less than half the finished width works best as that provides 'support' on both sides and reduces mill wandering/chatter. cut the long sides, then across the short sides, clean up the corners / end with a chisel.
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post #6 of 17 Old 10-31-2017, 04:38 PM Thread Starter
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Thanks for the responses so far.

First, I should have stated up front that nothing about these materials is "square", being that I used unsurfaced reclaimed wood. However, I can clamp them into a jig with shims to securely hold one of the faces perpendicular to the cutting device. Sorry about omitting that important point!


Quote:
Originally Posted by TomCT2 View Post
<snip> I have a cheap (HF) X-Y vice aka cross slide that I bolt to the drill press table + end mills.
in this case extra long end mills like
https://www.the-carbide-end-mill-sto...ongLength.html
<snip>a diameter well less than half the finished width works best as that provides 'support' on both sides and reduces mill wandering/chatter. cut the long sides, then across the short sides, clean up the corners / end with a chisel.
That's an interesting idea, I've never heard of that kind of vice nor an end mill. So you just chuck the end mill bit into the drill press, and use the vice to slowly feed the workpiece through, taking multiple passes until the full depth is reached?


A few of you mention flipping the piece over. I'm hoping to avoid having to do this, given that the wood isn't square and it would be more difficult to achieve proper alignment. But...if nothing can do the full depth in a single pass, I'll investigate the "flip over" options more.
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post #7 of 17 Old 10-31-2017, 06:03 PM
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lots of cross slide options here:
https://www.amazon.com/cross-slide-T...Across%20slide

an "end mill" has cutting edges on the bottom as well as along the flutes. they're probably more common in metal working - but they do wood just find. fewer flutes = faster cutting, more flutes = finer cutting. for soft wood I use 2 or 3 flutes, for hard stuff like rock maple I use four.

you want more/faster rpm on the mill than typically used for drilling holes - but yup, chuck it up like a drill bit, spindle down 1/4 - 3/8 into the wood, lock the spindle, crank the slide. both slides should have a locking mechanism - be sure to "lock" the non moving slide so vibration doesn't result in moving in the 'across' direction.

it's not rocket science - one practice piece and you'll be expert. just remain patient - pushing it too fast is not a good approach.
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post #8 of 17 Old 10-31-2017, 06:30 PM
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Here's my $.02.

People have made mortices like this for hundreds of years, by hand, using nice sharp morticing chisels. It's not that hard, and it doesn't take long to do it. Get some good morticing chisels, learn how to sharpen them, watch some videos, and have at it. You'll be done quickly and have satisfaction of knowing you did it all yourself.

... turning perfectly good wood into firewood every day ... :smile3:
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post #9 of 17 Old 11-11-2017, 11:20 AM Thread Starter
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Checking in with a progress update, and a couple of questions for you guys. Sorry for the long-winded post...basically I just need your opinion on the looseness of the MT joints. They will be keyed (tusk tenon) so the table base can knock down.

So first off, this was more time consuming than expected - and definitely a case of "the tortoise wins the race". I'm glad I did it though and look forward to doing a better job next time!

I went with the drill press method using a forstner bit from both sides of the through mortises. I drilled the corners using a longer brad point - the exit holes served as alignment marks for the opposite face. That all worked well enough. However, after a series of "learning experiences" while paring the mortises to their final size, I wound up with looser joints than I'd like. The insides of the mortises aren't perfectly flat or parallel to opposite faces and there are gaps in the joint as a result (both visible and hidden). I would guess the gaps average 1/16 to 1/8", but inconsistently, so I cant just insert a thin shim

I've attached photos showing how the looseness translates into unconstrained movement of the legs. They can be rotated several degrees before encountering resistance (compare photos 2,3). The entire base can be "racked" such that the top would move a full inch before resistance (photo 1).

What do you guys think? Should I consider enlarging the mortises (accurately this time) and either cutting new tenons on a new stringer, or reinforcing the tenons on the current board by laminating new material onto them? If so, what's the trick to enlarging the mortises by abouy 1/4" all around? My biggest difficulty was using a chisel to pare away the scalloped edges left by the forstner bit, is that something that just comes with practice or was I using bad technique? I held the chisel vertically and tapped it with a hammer. Used a 1" wide chisel. This is knotty oak and I kept my chisel as sharp as I could, but it was still gouging and tearing the fibers and trying to follow the grain. Crappy chisel?

I'd really appreciate your advice! Worse comes to worse I'll simply add diagonal reinforcements to constrain racking, and a 1x12 across top of the base to constrain rotation. But I'd be much happier if I can improve the fit of the keyed mortise and tenons!
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post #10 of 17 Old 11-11-2017, 02:25 PM
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Once you have a top fastened the racking and movement should be constrained, even when allowing for expansion.

Wise men speak because they have something to say; fools because they have to say something -Plato

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post #11 of 17 Old 11-11-2017, 03:14 PM
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Once you have keyed the tenons, the racking should be all but gone.

... turning perfectly good wood into firewood every day ... :smile3:
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post #12 of 17 Old 11-11-2017, 06:12 PM
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as Chris said, once the keys tighten the joint, the major factor is any racking will be the fit of the horizontal shoulder to the vertical leg. you mentioned the stock is not square, etc - you may need to trim the shoulders to precisely match up to the vertical so there is no gaps.
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post #13 of 17 Old 11-11-2017, 08:04 PM Thread Starter
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Thanks for the feedback. It makes sense that the top will reinforce the overall structure. Same for the cinched down tenons. Luckily the shoulders are pretty wide and tall so that should help.

I'll just work on getting the tenon shoulders flush with the vertical leg surfaces and then not worry about the rest.

Thanks!
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post #14 of 17 Old 11-11-2017, 08:36 PM
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Quote:
Originally Posted by FrankC View Post
Once you have a top fastened the racking and movement should be constrained, even when allowing for expansion.
+1: I agree with Frank. It will make a big difference when the top is installed.

If you don't have time to do it right the first time, when will you have time to do it over?
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post #15 of 17 Old 12-27-2017, 05:08 PM
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Quote:
Originally Posted by jeremymcon View Post
I like my hand tools, so I'll offer this - make sure your stock is nice and square. Market the mortise on both sides of the piece. Drill part way through with any bit that'll go half way through - I'd use an auger bit in a brace because it's long and easy to keep square by eye. Or I'd use a bard point, or an auger bit in a drill. I'd worry about it a forstner bit wandering too and you really don't need a flat bottomed hole, so there's no need for the forster.

If it's a 1" mortise I'd use a 3/4" or 7/8" bit. Drill halfway through from both sides, being sure not to hit your layout lines with the bit. Then chisel to your lines from either side with a 1" wide bench chisel (if your mortise is 1"wide). Only chisel halfway down then chisel from the other side. Keep the walls of the mortise square or angle to the chisel just a couple degree inward to keep from having a hump in the middle of the mortise.
I had read that a Forstner bit was not prone to tear out of the other side. My experience has been that this is not true.

I am responding to your post to second the recommendation you posted (bold), that you only go half way through the wood. I had tried going all the way through after reading about the lack of tear out with Forstners on a few other sites.

But I also wanted to ask... Is the tear out on my workpiece so bad because it was soft wood (pine)? Or should I expect this on all wood types when using a Forstner?

Thanks
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post #16 of 17 Old 12-27-2017, 07:31 PM
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If you are getting tear out on the top, try drilling at a slower speed as you enter the wood.


In woodworking there is always more then one way to accomplish something.
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post #17 of 17 Old 12-27-2017, 09:46 PM
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Quote:
Originally Posted by blktoptrvl2 View Post
I had read that a Forstner bit was not prone to tear out of the other side. My experience has been that this is not true.

I am responding to your post to second the recommendation you posted (bold), that you only go half way through the wood. I had tried going all the way through after reading about the lack of tear out with Forstners on a few other sites.

But I also wanted to ask... Is the tear out on my workpiece so bad because it was soft wood (pine)? Or should I expect this on all wood types when using a Forstner?

Thanks

All drill bits will have tear out when going all the way through, unless you use a backer board.
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