# Trimming down an interior door



## speechflyer (Oct 24, 2011)

Hi Everyone !! My name is Eric and I am new to the site. This i my first post and I really need some help. I recently purchased a new slab oak veneer HC interior door for my downstairs bathroom. It is 28"x80"x1 3/8" - WxHxD respectively. My house is only 14 years old and this door needed replaced. The problem is this: The existing door and jamb is only 27 13/16"x80"x1 3/8". Essentially I am wanting to use my 1/4" shank straight bit and trim down 1/8" so the new door fits in the existing jamb. If I was to replace the jamb, I run into further issues with fixing framing, threshold repairs, etc. Is it possible to do so with a straight bit given the length of the bit is only 1" long. I think I would need to run the door through then flip it over to complete the other side. The test runs I have tried all have failed because it is not lining up and looks horrible. Any and all tips are appreciated and well taken. Thanks in advance.

Eric


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## jschaben (Jun 21, 2009)

speechflyer said:


> Hi Everyone !! My name is Eric and I am new to the site. This i my first post and I really need some help. I recently purchased a new slab oak veneer HC interior door for my downstairs bathroom. It is 28"x80"x1 3/8" - WxHxD respectively. My house is only 14 years old and this door needed replaced. The problem is this: The existing door and jamb is only 27 13/16"x80"x1 3/8". Essentially I am wanting to use my 1/4" shank straight bit and trim down 1/8" so the new door fits in the existing jamb. If I was to replace the jamb, I run into further issues with fixing framing, threshold repairs, etc. Is it possible to do so with a straight bit given the length of the bit is only 1" long. I think I would need to run the door through then flip it over to complete the other side. The test runs I have tried all have failed because it is not lining up and looks horrible. Any and all tips are appreciated and well taken. Thanks in advance.
> 
> Eric


HI Eric - Welcome to the forum
A flush trim bit of the proper cutting length would be a much better approach. A flush trim bit with a bearing on the end will follow a straight edge clamped to the bottom side of the door. 
A little more complicated way you could do it with the bit you have is to clamp a straight edge away from the desired cut line by a distance of one half the diameter of your router base plate minus one half the diameter of the bit you are using. Set the depth of cut to a little more than half the thickness of the door. Size that half of the door guiding the router with the base plate against the straight edge. After you get the first pass done. Reset the straight edge EXACTLY the same on the other side of the door and make the final cut exactly the same way. 
A third way would be to obtain a bit made exactly for this purpose. Rockler, MLCS and others make a top and bottom flush trim bit. You put a smaller bearing on the tip and adjust the bit height so the smaller bottom bearing rides on the door edge. This cut will bring half or so of the door thickness to the right dimension. Then change the bit height so the top bearing rides on the surface just cut which will bring the door to the same size again. 
Lotsa options Good Luck


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## RJM (Apr 11, 2010)

speechflyer said:


> Hi Everyone !! My name is Eric and I am new to the site. This i my first post and I really need some help. I recently purchased a new slab oak veneer HC interior door for my downstairs bathroom. It is 28"x80"x1 3/8" - WxHxD respectively. My house is only 14 years old and this door needed replaced. The problem is this: The existing door and jamb is only 27 13/16"x80"x1 3/8". Essentially I am wanting to use my 1/4" shank straight bit and trim down 1/8" so the new door fits in the existing jamb. If I was to replace the jamb, I run into further issues with fixing framing, threshold repairs, etc. Is it possible to do so with a straight bit given the length of the bit is only 1" long. I think I would need to run the door through then flip it over to complete the other side. The test runs I have tried all have failed because it is not lining up and looks horrible. Any and all tips are appreciated and well taken. Thanks in advance.
> 
> Eric


Either get a longer bit, or use a circular saw with a decent blade (I would use a saw) .

Either way, you'll need a guide clamped to the new door. You can use anything that is straight (i.e. very straight) and will not interfere with the saw. You can buy an inexpesive 8ft long guide for $20 (usually comes in 2 pieces). If the old door has a straight side, you can use that for a guide.

Assuming the new door is straight, place one long edge of the old door against the a long edge new door. If there are no gaps, it's straight. If there are gaps (even small ones), try the other edge. Also, if using the hinge edge, make sure the mortices ar up - so the circular saw base will have a continuous edge to ride against. You may have to raise the saw slightly (i.e. reduce the cutting depth of the blade) so that the motor housing clears the old door (which would be clamped to the new door). Make sure everything will work before turrning on the power (i.e. dry run).

Also, rather you can use the old door as a pattern to mark the new door cut line to make sure you measured correctly and to check that the opening (jamb) is square. Often, older homes may have doors that have been modified (custom fit) to a jamb that wasn't square to begin with, or became out of square due to settling, expansion/contraction, etc. It would be a good ide to line up the hinge side of the old door with the hinge side of the new door and check the other 3 sides for squareness.


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## jlord (Nov 16, 2009)

speechflyer said:


> Hi Everyone !! My name is Eric and I am new to the site. This i my first post and I really need some help. I recently purchased a new slab oak veneer HC interior door for my downstairs bathroom. It is 28"x80"x1 3/8" - WxHxD respectively. My house is only 14 years old and this door needed replaced. The problem is this: The existing door and jamb is only 27 13/16"x80"x1 3/8". Essentially I am wanting to use my 1/4" shank straight bit and trim down 1/8" so the new door fits in the existing jamb. If I was to replace the jamb, I run into further issues with fixing framing, threshold repairs, etc. Is it possible to do so with a straight bit given the length of the bit is only 1" long. I think I would need to run the door through then flip it over to complete the other side. The test runs I have tried all have failed because it is not lining up and looks horrible. Any and all tips are appreciated and well taken. Thanks in advance.
> 
> Eric


Hi Eric.
A circular saw or table saw if you have one would be the best tool for this. You should trim your door more than 1/8". The door should be trimmed down to 27-9/16". Cutting it 1/4" narrower than the opening will give you an 1/8" gap around the door. Depending on the type of flooring or carpet you have you should also take off 3/8" to 1/2" off the bottom of the door. You cannot cut the door the same size as the opening it will not operate correctly.


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## speechflyer (Oct 24, 2011)

Thanks all for the fast responses. What I did was take the old door as suggested and used it as a long straight edge. I then took half of the base plate diameter plus half of the bit diameter, added them together and placed and clamped the straight edge that distance away from the new edge of the new door. I then ran it and then flipped over the door and repeated the steps above. All in all, I simply needed to sand the finished edge lightly and it fit right in. Here's something funny...After the cuts were done, I needed to trim up more of the door about 75% of one side. In other words, it was pentagon shaped and not square....Gotta love those cheaply built thrown togehter match boxes we call home here in the Chicagoland suburbs...Thanks again to everybody who helped offer some advice. Take care.

Eric


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## Mike (Nov 22, 2004)

Eric, these doors are often tapered to be slightly narrower on the inside edges. You wont see this just by looking; it will show when you put a square against it. This is to make it easier for the door to open and close. A couple years ago I had to cut down a hollow core door for a friend who was replacing it in a basement remodel job. Because of surface mounted duct work the door had to be shortened 8" for clearance. This removed the bottom support wood and without it the door would soon of warped. I cut a piece of 2x4" to fit in the cavity, applied some glue and a clamped it in place while the glue dried. This saved the customer an $85 custom sizing fee from the door company.


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## jschaben (Jun 21, 2009)

Mike said:


> Eric, these doors are often tapered to be slightly narrower on the inside edges. You wont see this just by looking; it will show when you put a square against it. This is to make it easier for the door to open and close. A couple years ago I had to cut down a hollow core door for a friend who was replacing it in a basement remodel job. Because of surface mounted duct work the door had to be shortened 8" for clearance. This removed the bottom support wood and without it the door would soon of warped. I cut a piece of 2x4" to fit in the cavity, applied some glue and a clamped it in place while the glue dried. This saved the customer an $85 custom sizing fee from the door company.


Hi Mike - Back bevel would typically be 2-3* depending on the thickness of the door. I've seen router bits just for that but the problem is with some of the older houses, the door frame may be tapered 7 or 8 degrees which makes the back bevel somewhat insignificant. I put new door stops in several rooms of my house. On one room I installed the door stops along the sides OK but the one across the top came up 3/8" short. I was sure I measured and cut it correctly. Problem was, I measured about chest height instead of climbing on the stool and measuring at the top:fie:

Hollow core doors are getting worse also. I've had several where I had to cut down and replace either the top or bottom support but my last one took the cake. There was no blocking for the latch assembly! I mortised out about 8" long by 4" deep and cut down a 2x4 block to glue in there to install the door knob:fie::fie::fie: The framing stock on those things is getting so thin now, I wouldn't be surprised if I don't have to start doing that for the hinges also.


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## Mike (Nov 22, 2004)

John, in the future you can save a lot of time using an Ames lock support. This heavy duty plastic device folds to insert through the knob hole and then springs back to give support around the hole. I have used them many times and they work great.


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## RJM (Apr 11, 2010)

speechflyer said:


> Here's something funny...After the cuts were done, I needed to trim up more of the door about 75% of one side. In other words, it was pentagon shaped and not square....Gotta love those cheaply built thrown togehter match boxes we call home here in the Chicagoland suburbs...
> Eric


Imagine that ...


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## RJM (Apr 11, 2010)

jschaben said:


> ... but my last one took the cake. There was no blocking for the latch assembly!


Could this ahve been a bypass closet door?


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## jlord (Nov 16, 2009)

RJM60 said:


> Could this ahve been a bypass closet door?


It probably was. They usually just get a recessed insert for a handle grab.


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## jschaben (Jun 21, 2009)

RJM60 said:


> Imagine that ...


Wasn't supposed to be.. Guy in the orange apron told me it was a interior hollow core. Wasn't till I already had the hinge mortises done and went to install the lockset I figured it out. Wasn't to big a deal, just irritating. I just clamped a couple of 2x4's on the door, added a couple of stop blocks. 5/8" bushing and 1/2" bit kept me out of trouble... What the bit didn't reach I just loosened up with a drill and vacuumed it out. Just cardboard anyway.
Thanks for the tip Mike.. I didn't know such an animal existed. Should have figured somebody would have come up with something by now though.


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