Hi Stanley, long time have not heard from you, it is nice that you are back.  In answer to your question it is a matter of preference in my opinion, as expense is one determining factor. Baltic birch is a stable and sound material of which to build a sled and will out last the MDF.  MDF has a way of self destruction if it is not handled with kid gloves, where Baltic birch will take many rough days of service.  If I was going to build one for my use I would go for the Baltic birch even though it is more expensive.

As far as plans again several factors will determine the type I would build,  Things like what is the purpose of its use.  What type table saw is it and how wide of surface do you have on each side of the blade and which side of the blade do you wish the accuracy to be built.  What several do not think about when they begin building a sled is that saw kerf is the alignment for the items being cut.  Meaning what side of the saw blade kerf do you want to use for aligning your cuts.  In a multiple track sled the off fall is determined by which side of the blade is the waste is placed.  Other wise if you want the waste to fall off on the right then use the left side of the kerf to set your material and just the opposite if the waste is to fall off on the left.  this is the fastest method as otherwise you will have to aline the cut by using the actual saw blade. 

The next thing to determine is do you want to use two miter slots (tracks) or use a single one.   The type of fence you want to use is also of importance.  Do you want to use one that pivots to allow you to cut different angles or is it going to be one that is a fixed fence built with the intention of cutting a 90 degree cross cut. 

if you want to use a sled that uses both miter tracks , before you build the sled determine that both tracks are aligned with each other meaning the same distance in the rear and in the front  at the extreme ends as if they are not you will have a sled that will bind in the tracks. 

Another thing to be certain of is do the blade and the miter slots run in the same plane so that the blade and the tracks are straight with each other.  If they do not then you will have a hard time making the sled run true to the blade and will have to make alterations to the fence and or the better way is to align the arbor trunion and arbor shaft making adjustments under the saw table.   Which ever side you decide to use as the waste side then make sure that you have the long open area on the opposite side.  In most instances you will be cutting off shorter pieces as the waste and will need the longer for the longer stock. 

Personally I have a several sleds build for different applications.  some are single track sleds and some are two tracks.   The one I use the most is one that is a single track sled of which has a  great degree of accuracy.   It is one with the adjustable fence.  I have one  used for cutting the notches in face frame construction of which has a wide opening for the wide tooth cutter and slides in two tracks.  I have one that is built for cutting 45 degree miters and slides in two  tracks and the type that has a "V" type fence to allow the cutting of both a right and left miter.  I have a sled that is built to cut a 90 degree cut with the table saw blade set at 45 degrees.  I also have some that cut at 22.5 degrees.  Something to realize that you can use a sled built to cut accurate 90 degree or other determined degree angle and use it to cut other angles and expect it to be accurate.  Each time you tilt the table saw blade to a different angle that it was built for you change the width of the saw kerf making it an in accurate table and fence.  The same applies to cutting different angles where you move the angle of the table saw blade and the fence as well such as if in cutting a compound angle.

In conclusion if you are wanting to use a sled as a cut off for 90 degree angles you can use either a single or two track sled where you cut the sled in half and keep the two pieces together by having a rear fence type that  holds the two sled platforms flat and together and one at the rear of which it has the same function.  A word of caution; Extra care must be taken with this time of sled as the blade can come through the rear fence and endanger the hands / fingers unless measures are taken to limit the travel of the sled across the table and also the keep the hands /fingers well above and out of the path of the blade.  Using this type of sled makes it difficult to cut an angle unless you build a set of angled templates of which you place between the fence and the material.  you are limited to the length of both the waste cut off and the length of the stock and is determined by the width of both the stock and the width of the sled.

This is why I use the single track sled with an adjustable fence as I cut many different angles when building some projects.  My sled runs in the left miter track so it cuts on the left side of the blade and leaves the waste on the right side of the blade.

One of the best resources that I have in mind if you desire to read and either purchase a sled or build one of which is not difficult is the company known as "In-line Industries"  the makers of the Dubby Sleds that are available at Rocklers .  hee is the web site as you can read and learn about the types of sleds;   The business is run by Jerry Cole who was part founder of the sled company several years ago.  He has an abundance of knowledge in precision cutting of angles and miters .

http://in-lineindustries.com/ 

Thanks Jay for your very detailed response.

What started all this was when I saw YouTube video of a sled being used by a woodworker up in the Northwest.  I sent him an email of where he got the plans and he refered me to the August 2008 issue of Fine Woodworking.  The sled was made out of MDF.  I ended up emailing John McCormack, the author the article of The Ultimate Crosscut Sled."  I asked him about why he used MDF in his design over Baltic Birch. His response was, "....MDF tends to stay flat, whereas baltic birch tends to be a bit of a potato chip."  Heck, I don't know.

My saw is a Ridgid R4510, portable contractors saw.  

It has been a while.  Was actually up "your way" in early July.  We stayed in Roseville one night on our way up the Portland area for our nieces wedding.  Life has been somewhat cray this past year and have not been here or on Lumberjocks that much.  Hopefully, that all will change soon.

I would like to build a sled with the Kreg Measuring System, amd it would be nice to be able to cut angles.

Thanks again Jay, let's stay in touch.

Stan

Thanks stan and i will stay in touch.  Wish yoiu would gave me a yell as you passed through as I would have loved to met you for at least coffee even if it was just for a few minutes.  You would have passed through my city.

As for as warpage of the birch. my experience with it tells me that it is stable as it is not like most plywoods as it is void free and multiple layers.  If it is sealed with a sealer of some sort I hight doubt that it would warp and become like a potato chip LOL.  John is correct about the MDF but I so far have not had the problem and I do live in the north west were the air is humid  a high percentage of the time.  Baltic birch is also used in many project that are exposed to water and humidity. 

You do have a nice saw and now building the sled will be a matter of choice as I explained in my post back to you last night.   Let me know if I can be of help to you and don't be stranger if you pass by again.

Stanley C. Pearse said:

Thanks Jay for your very detailed response.

What started all this was when I saw YouTube video of a sled being used by a woodworker up in the Northwest.  I sent him an email of where he got the plans and he refered me to the August 2008 issue of Fine Woodworking.  The sled was made out of MDF.  I ended up emailing John McCormack, the author the article of The Ultimate Crosscut Sled."  I asked him about why he used MDF in his design over Baltic Birch. His response was, "....MDF tends to stay flat, whereas baltic birch tends to be a bit of a potato chip."  Heck, I don't know.

My saw is a Ridgid R4510, portable contractors saw.  

It has been a while.  Was actually up "your way" in early July.  We stayed in Roseville one night on our way up the Portland area for our nieces wedding.  Life has been somewhat cray this past year and have not been here or on Lumberjocks that much.  Hopefully, that all will change soon.

I would like to build a sled with the Kreg Measuring System, amd it would be nice to be able to cut angles.

Thanks again Jay, let's stay in touch.

Stan