The Hammond G4B Trim-O-Saw are mounted a little differently than normal table saw blades. Consequently finding blades that will fit it is a bit more difficult than for a typical table saw.
This is the saw head on my Hammond G4B saw, as viewed from the side that blades are mounted. There is a round boss in the center that aligns the blade to the central axis of the spindle, three countersunk, 8-32 tapped holes for the mounting screws, and cutouts for the trimming bits, which are mounted on the arbor flange. A drawbar through the spindle threads into the central tapped hole to hold the saw head on the spindle.
The round boss on this head has an OD of 0.810" and any blade mounted on the saw must have a corresponding hole at it's center so that it can be accurately mounted on the head. The blade must also have 3 countersunk through holes to take the 8-32 screws that actually hold the blade to the head. No blades that I am aware of have these features as standard options. Consequently it is necessary to machine currently offered blades to fit the head, which involves boring out the central hole in the blade to fit the central boss and drilling/countersinking the screw holes. Options here are to do it yourself, find a local machine shop to do it for you, or find a supplier that will make the modifications.
This saw will primarily be used to saw plastic stock (acrylic, Delrin, acrylic, etc) for subsequent machining operations. My objectives are to cut the stock with better specs for squareness and edge finish than can be obtained with a 4x6 bandsaw or old 8" Craftsman table saw. Browsing the web, woodworking forums, and newsgroups revealed a couple of companies that had a good reputation for plastic cutting blades:
Forrest Blades and
No doubt there are other companies that make suitable blades, but a couple of limitations should be kept in mind. One is that any blade with a diameter greater than 7" will interfere with the fixed table in front of the arbor and another is that the smaller blades often seem to be configured with a diamond knockout for correspondingly shaped arbors. The knockout will intersect with the central hole that must be bored out for the saw head boss so a blade without this feature is needed.
Each company was called for recommendations. Forrest recommended their "No-Melt" blade and would modify it to fit my saw head, after requesting that I send them the one good HSS blade that came with the saw so that they could verify hole dimensions. They also made it special with a 7" diameter to avoid the interference mentioned above. Tenryu recommended their non-ferrous blade but could not do the modification and the smallest size available was 7-1/4". I ordered one of each to see which worked better for my applications. One possible side benefit of the Tenryu blade is that it can also be used to cut aluminum or brass sheet or plate.
The Forrest blade was $200 direct from the factory and including modifications and shipping. The Tenryu blade was a little less than $100, including shipping, from one of their mail order distributors. The Tenryu blade arrived in a few days and the Forrest took about 3 weeks.
The Tenryu blade had to be bored out and drilled and it's larger diameter required filing a small notch in the front part of the fixed table on the saw. Tenryu informed me that their blade plates are hardened but couldn't tell me to what degree. I assumed the worst and bought a 3/8" carbide countersink and #18 135° carbide drill bit made by Ultra Tool and sold by McMaster-Carr. The cost for these two came to around $40. My shop is equipped with carbide boring bits so there was no need to buy that.
The first thing I had to do was get the dimensions for the saw head boss diameter and the coordinates for the mounting screw holes. The boss diameter was measured with a digital caliper at about 0.810". A micrometer would have been a better choice for accuracy but the boss was too shallow to allow good placement of the micrometer faces against the OD of the boss. Then too, I planned to bore the central hole slightly undersize and then sneak up on it until a very light press fit was obtained for the boss. In that case accuracy to 0.0001" was not necessary.
The second requirement was to get the diameter for the screw circle. This was done by holding the saw head in a mill vise, arbor side up, and locating the arbor side boss directly under the spindle, setting the X/Y coordinates on the mill DRO to 0,0, installing transfer screws in each of the tapped screw holes and then using a pointed wobbler to visually line up the wobbler tip to each of the pointed transfer screw tips in turn. DRO readings were taken at each of the three screw hole positions and then average to obtain the mean screw circle radius.
Here the arbor-side boss is being center under the spindle with a Blake co-axial indicator. The Blake is a very handy tool for this purpose as the indicator face is always presented to the operator and the indicator is driven by the spindle so that the table can be moved in the X and Y axes to quickly center the boss under the spindle. A standard dial test indicator can also be used but the spindle must be rotated manually and the you will have to keep following the indicator face around the spindle to track the runout. Once centered, the DRO was set to 0 for the X and Y axes.
The wobbler tip is then installed in a collet, adjusted under power so that it spins true about the spindle axis, and then lined up with each of the transfer screw tips in turn. X/Y DRO readings were taken at each location. A small 10x loupe was used to aid in lining up the two tips. Transfer screws are available in a variety of standard screw sizes from vendors like McMaster-Carr. Very handy for this sort of thing, although most home shop machinists could cobble up something similar. The radius of the screw hole pattern came out to 1.025" +/1 0.001" which is more than enough accuracy for this application.
With the critical dimensions in hand, it was time to try modifying a standard saw blade. On the odd chance that I'd somehow screwed up a dimension or two, I decided to first modify a new, carbide-tipped 6-1/2" diameter blade made by Milwaukee and labeled "Endurance". This blade came to me in the original packaging with an older Craftsman 8" table saw bought used a few years ago. That went well and the blade fit the saw head perfectly so I proceeded to the Tenryu blade.
The Tenryu blade was clamped to a block of flat wood on the mill table for the boring, drilling, and countersinking operations. The block was drilled out in the center with a Forstner bit to provide a cavity for the boring bit. Once mounted the original blade arbor hole was centered under the spindle with the Blake co-ax indicator. Again this is done under power (I used 180 rpm) and only takes a minute or two. Here the arbor hole has been centered and the spindle is stopped to show a reading with the tip at about 3 o'clock.
Here the spindle is stopped at about the 9 o'clock position, roughly 180° from the position in the previous photo. As can be seen the indicator reading is nearly identical at the two positions. In use, the table is moved along the X and Y axes with the Blake under power until there is no or minimal movement of the needle on the Blake.
Here the alignment hole is being bored out with a boring head and import carbide bit. The blade plate cut easily and it may have been soft enough to have allowed boring with a HSS bit.
The screw holes have been drilled with a #18 carbide drill and are now being countersunk for the screw heads with a carbide countersink. I used fairly slow speed for this (350? and had no troubles at all with surface finish, although the bit did squeal a little.
These are the three blades I've got so far - the "free" Milwaukee Endurance (~$25 retail), the $100 Tenryu non-ferrous, and the Forrest-modified No-Melt.
The Endurance is a 6-1/2", 40-tooth blade, with staggered C3 carbide tips with ~0.072" kerf and designed for trim and finish applications. The Tenryu is a 7-1/4", 60-tooth blade with triple ground carbide teeth, 0.110" kerf, and designed for non-ferrous cutting. The Forrest No-Melt is a 7", 60-tooth blade with triple ground C4 carbide teeth, 0.092" kerf and designed for cutting plastic.
With the blades bought and modified as necessary it was time to try them out. I used PVC and acrylic flat stock as test pieces since this is usually the type of materials that I work with. PVC is usually easy to cut but acrylic can be a problem as it tends to chip easily.
These are test cuts with small PVC blocks, about 1" long. From left to right, the pieces were cut with the Endurance at very slow, slow, and fast feed rates, the Tenryu at fast feed and the Forrest No-Melt at fast speed.
These are pieces of 1/4" thick acrylic and about 3" long that were cut with the Endurance, Tenryu and Forrest blades (bottom to top) and all at fairly fast speed.
The finish from the Endurance seemed to be a little worse than that from the Tenryu and Forrest blades in both PVC and acrylic but all of them cut pretty cleanly with little evidence of chipping. For the money, and assuming that best finish is a concern I'd say that the Tenryu is the best value.
Last edited: 07/23/2005