Central Machinery is the brand name for Harbor Freight Tools---who sell Chinese made knock off design tools. Some of their tools are simply exact copies of name brand models in a different color---even parts interchange. The tools/parts are made as cheaply as possible, however, and Customer Service is simply replacement under warranty.

You might look in a HF catalog. Otherwise, it will be luck.

Hi,
Maybe a 1/8" bushing is called for the install the 5/8" bits in the 3/4" collet. That's the way the grizzly mortiser works for the different sizes of chisels in the range from 1/4 to 5/8 diameter.
Casey

First let me say that the mortising chisel and bit set must be matched. The gap between the chisel and bit must be such that the chips created do not get hung up between them. The density of the wood also plays a part as well but I do not know the details on that.

Now the 3/4 shank on the mortising chisel is a common size but there are others. Buying a chisel and bit set is like buying a replacement drill bit, the make of the machine has no bearing on it. They are listed for sale at most places by size and depth of the mortise you want to make. The other dimensional details are all variable and up to you.

Woodcraft Supply has many sizes for sale. I have included a URL link.

http://www.woodcraft.com/family.aspx?familyid=8313&mode=details#tabs

Also if you are unfamiliar with setting it up this link has a good article.

http://www.newwoodworker.com/setupmort.html

Here is a link that might be useful: Woodcraft Supply

3/4" shank mortise sets...

http://www.woodcraft.com/family.aspx?familyid=8313

Here is a link that might be useful: woodcraft mortise sets