Finished the last manual machining part! The grinder is now assembled and operating (albeit with no electronics housings) for testing and debug. This post is a catch-all for the various small grinder components which, although important, do not fit neatly anywhere else. The tracking and tension systems are in this category.
Pretty much all of these parts started out 3D printed for testing purposes. For the spacers and spring holders that worked out pretty well. I suspect those components could have been left as PLA pretty much indefinitely. The tracking adjust and hold-down plate on the other hand broke pretty consistently while fitting up the rest of the grinder.
Components of the tension system. The two pieces on the left are spring guides, and the piece on the right is a pivot block for the hold-down-arm.
All of the various brass spacers cut to set tracking. (Including one spare used for the electrical control box).
Tracking System:
The tracking wheel is placed on a pivot, whose set point is adjusted by turning a 1/2-13 knob on the side of the grinder. This very slightly changes the tilt of the tracking wheel, and thus allows the user to move the belt right or left along the grinder platen. This is useful both for tuning in any slight misalignment in the grinder setup (though there seems to be very little) and as a way to get easier access to the belt edge for cutting tight corners.
The wheel itself is mounted to a CNC machined plate, which rotates on bushings about a 1/4 in steel shaft. That shaft is then spaced away from the tension army by a pair of clamps. This setup works well, although if I were to make the grinder again I would likely replace the four clamp pieces with two solid standoff blocks, and replace the 1/2-13 threads with 1/2-20 for finer adjustment.
Spring Guides:
The belt tension for the grinder is provided by a spring which pushes up against the tracking arm. It is held on either side by one of two cylindrical spring holders which are connected to their respective bases with 1/4-20 screws. Both parts were turned on a Southbend lathe and then given a light brushed finish with skotchbright. The upper tracking plate was then transferred to the mill in a collet holder so that the flat and threaded hole could be added. A fixed lower spring guide does introduce non-linearity to the force per unit compression, but also greatly simplifies assembly by helping constrain the spring.
Note: This was one set of parts which really could have stayed 3D printed. The plastic versions held up well during testing. With that said, a failure of the tension system mid-grind would have been bad…
Hold-Down Assembly:
This is an idea I borrowed straight from Reeder Grinders, although it shows up on a number of builds in various forms. To hold the grinder in it’s untensioned position, the hold-down plate can be flipped up with the arm lowered. Then, to release the tension arm, the user simply pushes the arm further down, allowing the hold-down plate to fall aside. This is particularly useful for switching belts, since it means the user does not need to hold down the tension arm while installing or removing a belt. However, the real reason I have this system on the grinder is that it ensures consistent belt tension. Because the arm is always released at a specific height (set by the hold-down block), the spring is always compressed by a consistent amount. Based on the manufacturer recommendations for my belts, and some testing, I have set this force to be 35lbs.
Alignment Spacers:
Spacers for setting the alignment of each wheel. These were turned on a lathe to +5 thou and then sanded to final dimension.
