miter saw at 45 degrees issue?

I am cutting some rectangular shaker style base boards for an outside corner at 45.
the board is 3/4" thin and 4" tall. When i cut it at 90 and match it to a square its perfect.
when i tilt my blade to 45 degree and cut im off by a 1/16th at the bottom. so its a slanted cut. tight at the top and off at the bottom.

what am I missing? the blade seems perfectly aligned until i get on an angle.
its a kobalt brand 10" compound sliding dual bevel saw. Could it be the saw?
The blade is a diablo 90 tooth.

i tend to be a perfectionist doing things like this. i know most would caulk the joint and call it a day. just not sure if theres a problem here or if im asking to much of a lowes DIY grade saw.

any suggestions?

 

When you cut at 90 degrees, you only cut 3/4 inch . When you cut at 45 degrees, you cut 4 inches. Therefore you get 5x the error in the 45 degree cut. Is the 45 degree position location keyed like a pin in a hole or a v groove? Can the key not be engaged and set manually?

 

I dont know that saw but on my DeWalt there are adjustments that can be made to fine tune the angles.

If its a cheap saw that option may not exist and you will have to set it manually!

 

I'm assuming that you are making a vertical cut. Have you checked the saw for perfect vertical? If that's OK try clamping the board to your fence when you cut.

 

The answer depends on if you are talking about a miter or a bevel and whether you are standing the base up with its back against the fence or if you are laying it flat on the base plate as you cut it. Either way it's likely some adjustment that needs to be made. If the wood is warped and not laying perfectly flat as you cut it will also act like the saw is off.

 

I think im doing a miter cut? I put the piece of trim up against the fence, clamped as suggested and make my cut down through the MDF at a 45 degree.
the miter does have keyed stops, but the bevel is tricky to get zero.
I finally got it to zero using a square, but im still off just a tiny bit. I think its because the cabinet wall and the floor are probably not a true 90 degree. Here are some photos to help.
you can see the final product which i glued and taped at the corner until dry then brad nailed. I will finish with caulk. its very close, but not perfect which is always my goal.

 

You have trouble when you assume corners are 90 degrees. If you take a framing square and put it on the corner you will be able to tell if it's square or not.

Plus, drywall corner bead (on outside corners) and mud and tape (on inside corners) really throw things off. Drywallers often leave big gobs of mud on the bottom of walls that don't get sanded down... its up to the trim carpenter to shave this off with a chisel before he trims. To be more accurate, you could also get a Starrett 505p-7 miter protractor. It measures the angle and then even tells you what the bisected angle should be. Handy tool to have around for trim carpentry.

Titebond has a white wood trim glue that I like to use on white prepainted trim.

 

I like to apply caulk when I make the joint rather than after. I think it provides more surface to adhere to than injecting it after.

 

I apologize for jumping in late.

Male sure the stock is held securely during the cut. Any movement or "crawl" will cause the condition you describe.