Can't get my dado stack to the right dimension.

[photobug]

As part of setting up my new-to-me Unisaw, I am trying to make a crosscut sled and want to put t-tracks in the top surface.  I have been trying to get the dimensions correct but the setting seems all over the place.


I try one set up with a stack of shims and it is too wide, so I walk around the saw duck under my miter station unplug the saw, raise the blade and remove the nut, remove two tiny shims and put the stack back on, drop the nut in the sawdust filled cabinet, magnet does not find it so have to vacuum out the cabinet, install, plug the saw back in, make a test cut and find the dado is too narrow.

I go through the whole process again and add a tiny shim and the dado is now 1/16" too wide.  After about 2-3 tries with the change in dado width not corresponding to the shim change I keep trying without unplugging the saw in between, because I am tired and frustrated at this point.  Eventually I call it a night in the shop and go online to browse for a new dado stack before going to sleep.

Before you ask, yes I had the blades and cutters aligned so the kerfs did not affect the stack.  I think the problem is the arbor holes on this dado stack is very tight and the plastic shims are getting caught up in the arbor threads.

Would a new set of shims make this easier?  

Is there a trick to getting this right?  

Which dado stack should I look at when I give up on this one?

[gregr]

As part of setting up my new-to-me Unisaw, I am trying to make a crosscut sled and want to put t-tracks in the top surface.  I have been trying to get the dimensions correct but the setting seems all over the place.


I try one set up with a stack of shims and it is too wide, so I walk around the saw duck under my miter station unplug the saw, raise the blade and remove the nut, remove two tiny shims and put the stack back on, drop the nut in the sawdust filled cabinet, magnet does not find it so have to vacuum out the cabinet, install, plug the saw back in, make a test cut and find the dado is too narrow.

I go through the whole process again and add a tiny shim and the dado is now 1/16" too wide.  After about 2-3 tries with the change in dado width not corresponding to the shim change I keep trying without unplugging the saw in between, because I am tired and frustrated at this point.  Eventually I call it a night in the shop and go online to browse for a new dado stack before going to sleep.

Before you ask, yes I had the blades and cutters aligned so the kerfs did not affect the stack.  I think the problem is the arbor holes on this dado stack is very tight and the plastic shims are getting caught up in the arbor threads.

Would a new set of shims make this easier?  

Is there a trick to getting this right?  

Which dado stack should I look at when I give up on this one?

I make shims out of an old deck of Bicycle brand plastic coated playing cards.  The cards measure about .010 and the thickness is very consistent from card to card.  I use a gasket cutter to cut the outside diameter, but they could easily be cut out by hand with scissors.  I use a 5/8" forstner bit to make the arbor hole.

HTH
Greg

[Roly]

Try putting TOO many shims in place so the cut is wider than you want.   Make a test cut in a sample board, the place the runners or the item you want to fit in the slot, remove the shims you put on the arbor and place a few of them along side the item in the slot until you get the fit you want.  Set them aside and install rest of shims that were on the arbor.     
 Unplug the saw when changing blades, if you get too tired or aggravated to do this it is time to stop.   Roly

[rwe2156]

Probably a shim issue, not the blade set.

Had the same issue, I traced the problem to the shim (especially very thin ones) falling into the screw thread and not seating right.

I had this issue when using brass shims when I switched to steel shims no more problems.

Hope this helps.

My technique for determining stack width is to simply lay the blades down flat on your ts top and either measure the height, or make it flush with the inserted piece.

[Alan S]

If it is a problem of shims dropping into the threads, magnetic shims can help.  The problem is that they are not thin enough for very fine adjustments, so you will likely need the brass shims too.  If there is a little unthreaded space on your arbor, sometimes you can get away with putting the fine shims only immediately after the first blade (on unthreaded arbor), then use magnetic shims that won't drop into the threads for any larger adjustments.  

Dial calipers used with a little table of kerf widths with various chippers can get you within a couple of thousandths the first try.

[photobug]

Thanks for all the suggestions. I tried one more time this morning and with the caliper it looks right just needed my wife to wake up to fire the saw, our bedroom is over the garage.  The dado and shims are nearly 20 years old at this point and the cheap plastic shims have always been a pain.  Yes they are getting in the threads making adjustment impossible.

Any suggestion on where to find steel brass and magnetic shims?

Baring getting the shims I have now to work I will try the playing cards in another way.  I will try and auxiliary fence and under size the dado then shim it out for a second cut with playing cards.

[Admiral]

Thanks for all the suggestions. I tried one more time this morning and with the caliper it looks right just needed my wife to wake up to fire the saw, our bedroom is over the garage.  The dado and shims are nearly 20 years old at this point and the cheap plastic shims have always been a pain.  Yes they are getting in the threads making adjustment impossible.

Any suggestion on where to find steel brass and magnetic shims?

Baring getting the shims I have now to work I will try the playing cards in another way.  I will try and auxiliary fence and under size the dado then shim it out for a second cut with playing cards.

Why don't you just cut the two sides of the dado accurately with a regular saw blade, then either reinstall the dado blade to plow them out, or nibble the interior away with the single saw blade, and finish up with a router plane.

[Ray Newman]

Magnetic dado blades shims:

https://www.highlandwoodworking.com/magn...shims.aspx

http://ridgecarbidetool.com/accessories/...m-set.html

https://www.amazon.com/s/?ie=UTF8&keywor...l8ywschp_b

https://www.forrestblades.com/accessories/magnetic-shims-set/

[blackhat]

A 3/4 router bit and a straight edge guide if you can't do it on the router table?

[photobug]

Problem solved.

I remember the thin shims and tight arbor holes on my dado being a pain to use.  So I blamed my current sizing issue on the stack and have ordered new shims.  Eventually I had removed all the shims on this stack and carefully tightened up the arbor nut and it is just a hair too wide.  I then remembered the board I was using for test cuts had already had a test cut dado in it from my 3/4" ply router bit.  When I ran into the problem with a too narrow cut, I realized now I was testing the old plywood router bit cut.  New policy is to mark each inaccurate cut with a black marker as to not confuse old test cuts.