How much to Dimension

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Forum topic by Bluebeep posted 08-10-2020 09:03 PM 405 views 0 times favorited 7 replies Add to Favorites Watch
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2 posts in 42 days

08-10-2020 09:03 PM

Topic tags/keywords: beginner question

Hi guys,

Not sure if I have posted this in the right place.

I’m a new woodworker and I have been battling a question as I have started on a new project. I got myself a power planer which can do both dimension and finish planing. I’m working on the arm of an outdoor chair that has a finished dimension of 70mm thick in my design.

I have some mortise and tenon joints that I need to cut out in the arm so I was thinking maybe I should get the initial dimension to around 75mm, cut out the joinery, then I have 5mm for finishing.

But doing it that way would make the joint 5mm off.

So the other option is to cut the initial dimension to exact proportions and cut out the joinery. But that means there won’t be any room for finishing.

I’m not sure what the normal approach is to this and I need some guidance.

The best I can think of is to make the initial dimensions super close to say around 72mm leaving me 2mm for finishing and hope that when I put the joinery together the compression of the wood will take on that extra 2mm.

By this I mean say I make the mortise 25mm deep, when I finish the piece it may take out 1-2mm meaning the mortise will now be around 23mm or so. And if the tenon is at 25mm it would mean I would hope that the 2mm extra on the tenon will compress into the mortise.

For sure I could make the tenon 2mm shorter but I’m not sure what the normal way of doing things is and I’m hoping to grab a rule-of-thumb so I can form good habits.

What are your thoughts? How do you guys handle this?

-- It's not about the type of Drum you've got, or how expensive it is. It's how you beat the Drum that makes people move.

7 replies so far

View bilyo's profile


1161 posts in 1951 days

#1 posted 08-11-2020 01:46 AM

Sorry. I’m confused. Not sure what you mean by “not having room for finishing”. Some sketches or photos would help greatly.

View Woodknack's profile


13471 posts in 3228 days

#2 posted 08-11-2020 08:42 AM

Everything after, “But that means there won’t be any room for finishing,” is confusing. But definitely make the tenon slightly shorter than the mortise is deep to allow space for glue otherwise the hydraulic pressure of the excess glue may prevent you from closing the joint.

-- Rick M,

View ChefHDAN's profile


1730 posts in 3698 days

#3 posted 08-11-2020 10:31 AM

I’m guessing you have the DW735 with 2 speeds, dimension-ing & finishing speeds. Your goal off of the planer is to get to your final working thickness. If you’re thinking of getting close to dimension, cutting your joinery and then running that piece through the planer again, you’re headed for a heartbreak. Snipe chip out etc etc, can damage the piece, always keep your initial stock piece slightly wider and longer than needed and plane to thickness and then do the woodworking to create the pieces.

-- I've decided 1 mistake is really 2 opportunities to learn.. learn how to fix it... and learn how to not repeat it

View tomsteve's profile


1064 posts in 2067 days

#4 posted 08-11-2020 11:38 AM

i dont think ive read,seen,or heard of anyone that does m&t finish to size after making tenons.

View Bluebeep's profile


2 posts in 42 days

#5 posted 08-11-2020 01:26 PM

Maybe I’m just overthinking things. Making the tenon slightly shorter makes good sense!

Thanks guys!

-- It's not about the type of Drum you've got, or how expensive it is. It's how you beat the Drum that makes people move.

View Madmark2's profile


1608 posts in 1436 days

#6 posted 08-11-2020 03:29 PM

As a general rule you don’t want your tendons to bottom out. Better to be a hair short than any amount long.

-- The hump with the stump and the pump!

View Robert's profile


3936 posts in 2329 days

#7 posted 08-11-2020 03:38 PM

That approach won’t work.

If I’m understanding your question, generally, you do the joinery after final dimensioning. Depending on the application, surface prep can be done either prior to laying out the joinery, or after assembly.

A planer’s function is thicknessing. Even the best of planers will leave mill marks. They may not be noticeable until finish is applied – trust me on this ;-)

Although removing material from a mortised surface will change the final dimension after assembly, sanding, scraping or hand planing is usually just a few 1/thousands inches, so it’s not changing dimensions appreciably.

But it depends on the situation. For example, an apron that is offset to a leg, both surfaces can be prepped prior to assembly. But if the faces are flush, for example a door or face frame, you do the surface prep after to assembly.

If you have to take a little off a tenon it is usually of no consequence, as I said, were talking a few thou inches.

-- Everything is a prototype thats why its one of a kind!!

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