Wednesday, November 13, 2019

Pet Gate Design, part 1

In my last blog post I showed off my new pet gate - for the cutest puppy on earth.

I figured I would share the steps I went through and what calculations you might need to make your own gate.

Step 1: Determine the height of the gate

This is probably the easiest step. Figure out where you'd like the top of the gate to be and then measure to that point from the floor.

I wanted the top of my gate to be high enough that I could reach the top comfortably with an outstretched arm without requiring bending over. That was about the same height as the chair rail in my dining room so I picked that height which is 35" from the floor.

There's a small bull nose baseboard trim in the door opening that I figured it would be easier to just avoid versus trying to remove to make the gate swing closer to the ground. That sets the bottom of my gate about 3" from the floor.

Step 2: Measure your opening

The second step in knowing the size of your gate is to know how wide the opening it needs to fill.

You could use any number of super accurate techniques; however, I found a normal tape measure to be sufficiently accurate. Since no house is square or plumb it is smart to measure the width at multiple points between the bottom and top of the gate location. It would also be a good idea to check the openings for plumb.

I got lucky and found there was only a 1/8" difference in width between the top and bottom of my gate opening. That's small enough to just ignore or average into the gaps I'm putting into the design anyway. As an additional bonus I found that the wall I planned to mount the hinge onto was plumb.

My gate opening is 39" wide.

Step 3: Determine the gate final dimensions

Unfortunately there are a lot of dimensions to calculate. It is all simple math but we need to get a number of parts calculated and many of the parts are based off the size of other parts.

The overall gate consists of the following parts:

  • Handrail
  • Rails x2
  • Stiles x2
  • Latch block
  • Hinge Block
  • Balusters x8
In the diagram above you can see the overall dimensions of the gate. and the positions of the parts. That's enough to start making calculations.


The only dimension that the handrail affects is the height of the gate body. I wasn't sure what I was going to make it out of when I started but I knew I wanted it to be a little thicker than other parts so I decided on making it 1" thick.

Rails and Stiles

The rails and stiles should be the same thickness (mine aren't but it all works out in the construction techniques). I did all my original calculations at 1" thick for both of these parts but they actually ended up at 3/4" after jointing and planing. The diagram above shows them at their actual thickness but explains why the outer gaps between the balusters and gate are slightly wider than the rest.


The height of the stiles is the total gate height minus the thickness of the handrail. In my case it was 33"

[Stile Height] = [Total Height] - [Handrail Thickness]

34" - 1" = 33"


The length of the rail is a little more complicated. It overlaps with the hinge block to allow pins from the hinge block to form a pivot point. I knew from the beginning that I was going to need to round over the end of the rail to avoid pinching the corners against the wall when the gate was opened. To give myself some insurance against pinching I wanted a 1/4" gap between the wall and the rail. On the latch side I wanted a 1/4" gap between the latch block and the gate, again to prevent pinching.

That gives me the following calculations:

[Rail Length] = [Opening] - [Latch Block] - [Latch Gap] - [Hinge Gap]

39" - 1" - 1/4" - 1/4" = 37-1/2"

Latch Block

I decided to make my latch block an inch wide. I thought it would look good in proportion to the gate parts and would be thick enough to give my latch mechanism something to grab a hold of. I didn't determine the final height until the gate was finished but I ended up thinking it looked best if it was the same height as the body of the gate at 33".

Hinge Block

The hinge block needs to be captured between the top and bottom rails and I added a little bit of a space to make sure there's no binding. The length of the hinge block is the height of the gate body minus the rails and the gap.

[Hinge Height] = [Gate Body Height] - [Top Rail] - [Bottom Rail] - [Gap]

33" - 1" - 1" - 1/4" = 30-3/4"

That gets us the height of the hinge block, but how wide to make it? I'd decided to make my gate body 1-1/2" deep That means for the gate to swing fully open and with the hinge pin centered on the top rail I needed the pin to be 1" from the wall. That's half the width of the top rail [3/4"] plus the gap between the top rail and the wall [1/4"]. Since I wanted the pin in the hinge to be centered(ish) I needed another 3/4" to the width (the other half the width of the rail).

I also needed to round over the side of the hinge "barrel" to avoid pinching when the gate opens.

The diagram above is a cross section of the hinge barrel. The block before shaping is 1-3/4" x 1-1/2" x 30-3/4".


Maybe these are the simplest parts. I wanted the gate to be lightweight and I figured that 1/2" thick balusters would be plenty strong. I decided to make them 1/2" square because of how I was going to fix them in the top and bottom rail. More on that in a little bit. I wanted to keep the balusters legal for a handrail which is that the gap between spindles cannot be greater than 4", for this I needed to calculate how many balusters to make. 

To calculate this I need the size of the gate body not counting the extensions for the hinges. That's going to be the length of the rail, minus the overlap between the rail and the hinge, minus the gap between the hinge and the gate and the gate stiles.

[Gate Body] = [Rail] - [Hinge Overlap] - [Hinge Gap] - [Left Style] - [Right Style]

37-1/2" - 1-1/2" - 1/4" - 3/4 - 3/4 = 34-1/4"

That math gives us 34-1/4" between stiles. Dividing that by 4 gives us about 8.6. This is the number of gaps in the gate. Since we cannot have a half gap we round the number up to 9. To get the final spacing of the balusters we divide the 34-1/4" by 9. This gives us a final gap size of 3.8.

But wait! Why didn't you need to take the width of the balusters into account?

To make double sure that my gaps were small enough I'm going to space the balusters 3-3/4" on center.

Step 4: Parts List

All the math is done. The rest is writing down a parts list and rough cutting the parts. My gate is going to be 1-1/2" thick. 

PartDimensions (h x w x l)Count        Material
Handrail                xxx    1  Walnut
Rails3/4" x 1-1/2" x 37-1/2" (*)                2  Poplar
Stiles3/4" x 1-1/2" x 33"    2  Poplar
Latch Block1" x  1-1/2" x 33"     1  Poplar
Hinge Block1-3/4" x 1-1/2" x 30-3/4"    1  Poplar
Balusters1/2" x 1/2" x 33"8 (**)  Poplar

(*) The rails need to be cut a little extra wide for machining
(**) I made a couple of extra balusters so I could pick the best for assembly


With the design complete and the parts list written all that's left is construction, finishing and installation.