Having owned a Delta Contractor's saw with a 30" Unifence and having recently upgraded to a Delta Unisaw with a 30" Biesemeyer fence I think I can offer some insight to the question on the difference between the two fences.
First of all, having owned and used both fences, I can say that you can't go wrong with either, they are the best of the best. Second, don't bother with the home shop versions of either. The commercial versions are just a little bit more expensive and for the money you're paying for a quality fence would might as well pay the extra 10-20% to get the hefty version. Dust doesn't affect either, they are both very well designed and dust doesn't affect their accuracy or alignment at all.
The Unifence is made almost entirely out of heavy aluminum. The front rail attaches to the front of the saw and the extension table board attaches to the saw's cast iron table and to the front rail. There is no supporting piece at the back. For these reasons I wouldn't use a Unifence of any size without legs supporting the extension table.
The Biesemeyer rails are made of heavy strong steel. There's a supporting piece in the front and the back and then the rail tube mounts to the front rail piece. So there are 3 pieces of steel supporting the extension table. The Biesemeyer fence rails are strong enough to support the extension table without legs. Having said that I must say.... NEVER HAVE AN EXTENSION TABLE WITHOUT LEGS. Just imagine the damage that would be caused if you tipped over the saw. At some point, you WILL put something heavy on the extension table, either a stack of wood that you don't have space for immediately, or something like that.... and bingo your 250-500 pound saw will be on it's side.
Both are very well designed fences. They are different mind you, each being a little better in certain areas than the other.
The Unifence is a little more versatile. The aluminum fence is actually two pieces. The T portion that attaches to the front rail and the actual fence. This design allows two things. You can slide the fence towards you so that only a small portion of the fence is actually on the table. This allows you to crosscut with your miter gauge safely since you can place the fence end before the blade starts. When crosscutting with a miter gauge you have the risk of kickback if the piece to the right of the blade turns slightly and jams between the blade and the fence. On any other fence you'd have to place a small block of wood against the fence to give you a gap next to the blade. Also, the Unifence can be switched so that you have a very short fence. I never used it that way but it may be a useful feature to some people.
The drawback to the Unifence design is that if you want to be use the fence on the left side of the blade you have to remove and re-attach the fence to the other side of the T. It's really easy to do but the Biesemeyer has a fence face on either side. Also because the Unifence is not symmetrical you can't make certain jigs that will ride on the fence. Also it's a bit more difficult to attach hold downs, etc. to the Unifence. Unifence is lighter so it is a bit easier to move, but it's lightness is also a drawback in my opinion.
The Biesemeyer fence is more solid. The rails are stronger. The fence is heavier and stronger. It is bullet proof! It also has the double faced fence. The reason I chose the Biesemeyer fence over the Unifence the second time round was for it's strength and durability. I was always a little worried that I would dent, ding or scratch the aluminum fence or rail on the Unifence. I bought my Unisaw to last a few generations and know that the Biesemeyer will keep up with it. I feel that the Unifence, because it's lighter and aluminum, would age earlier.
For either fence, the extension table doesn't come with the fence and it's pretty expensive for what it is. $60-$90. I made mine. Using good quality plywood or MDF and some hardwood braces, contact cement a a piece of Formica, you can make a very nice extension table yourself. On hint if you go with the Unifence: make the table 1" bigger (28" if your saw if 27" deep) and place a square steel tube along the whole length back of your saw and under the table to give it extra support and help keep it straighter.
I like the Biesemeyer better but, again, you can't go wrong with either of these.
|A Biesemeyer fence is a shiny silver dollar coin and a Unifence is a crisp new dollar bill.
A Biesemeyer fence is a shiny silver dollar coin and a Unifence is a crisp new dollar bill. One's a little more solid than the other one's easier to fold into your wallet. They're equal in value. Just with a few difference that make them appeal to different people.
Fences come in several sizes but 30" and 52" (measured by the ability to cut that distance from the blade) are the most common. If you have enough space in your shop the 52" size is handy if you cut a lot of plywood sheets. If you have a small shop, like I do, you may prefer to buy the 30" fence and use the money saved to buy a mobile base for the saw. I've owned the 30" Unifence and now have the 30" Biesemeyer and have never wished for more capacity. In the very, very few cases I've needed to rip plywood more than it could handle, I prefer to make the cuts with a 7-1/4" saw first, and then do the final cutting on the saw. Plywood, etc. is too heavy for me to enjoy cutting on the table saw in one piece so cutting it down to size is fine for me. I don't do it very often because when I do by sheet goods I usually get the vendor to cut them down to manageable sizes first.
If you have space and money 52" is good, but if you don't have the space you may be happier with the 30" and a good mobile base. I personally bought the 30" Unifence on my first Delta contractor's saw and then bought the 30" Biesemeyer when I upgraded to a Unisaw.
Benefits of 30" - Regular mobile base will work. Fence is strong enough to support table when raised by base. When down the table rests on the legs to prevent tipping. This will save you at least $90 over buying the extended mobile base. Unless you 're lucky enough to have unlimited shop space, the 30" model takes less space and is easier to maneuver around on the mobile base.
Drawbacks and solutions: - You are limited in the size of plywood you can cut. For instance you can't cut a 8'x4' piece of plywood into 4'x4' (you can rip it to 2'x8' or 2-1/2'x8 easily though). For me I rarely do this, plywood is too heavy for me and I'd prefer to get the lumberyard to cut it down to workable size. If I need to cut it, I simply use a 7-1/4" circular saw to cut it down to manage size and finish it up on the table saw.