Belt Grinder: Electrical Housings

The grinder is done! I’ve got some ideas for new things to add and additional tweaks to make, but as far as the core build is concerned everything is finished, running, and ready for use.

The grinder uses a 1.5hp Iron Horse connected to a 6” drive wheel. The motor is controlled using a Kbac 27-D VFD configured with variable speeds, reversing, and a momentary-start switch.

With a custom front plate the KBAC just about fits between the vertical pivot supports. I moved the controls to a separate box, mounted to the front of the grinder. The main VFD box is sealed against grinding dust with a locktite liquid gasket, and all of the cabling passes through water tight glands. The cabling is standard industrial cabling from Mccmaster Carr and is covered in replaceable cable sheaths to protect against abrasion.

The front plate, after brushing but before installation.

VFD:

The variable frequency drive (VFD) which controls the main motor is located between the two vertical pivot arms. To accomplish this I added a horizontal bar on the rear pivot arm, and replaced the front VFD lid with a much thinner custom panel. The horizontal bar was constructed of the same 1/2 by 2 aluminum extrusion that was used for the arm plates, and the front cover was blanked out of spare 1/2 inch aluminum plate using the waterjet.

After blanking, the front plate was machined on the Haas to add the gasket groove, counter bores, and display features. I also removed most of the material from the center of the plate to provide a bit more room for internal wiring (It’s tight, but fine). One particularly fun feature of this part is the display area. I included mounting geometry for the original LED board, and turned some acrylic plugs to pass light from inside the box.

Photos really do not do the control box justice. This is one of the nicest pieces I have ever machined.

Control Box:

Mounting the VFD between the grinder legs means there is no way for the user to interact with its normal switches and knobs. This control box allows the speed control, direction control, and start switch to be mounted directly on the front of the grinder where they are easily accessible to the user.

The box is machined out of a single piece of 6061 aluminum, and is mounted to the grinder by four 4-40 screws, which connect to the box’s rear cover plate. The dial design is based on cockpit of a DC10, and the engraved lines have been filled with lacquer to help them pop. All of the controls are sealed against dust, as is the gland that permits the control cable to enter.

The lacquer sticks are a new technology for me, and I was pleasantly surprised by how well it worked. Getting good results took a bit of practice, but was otherwise quite painless. The method I settled on runs as follows. First, use the sticks to cover the engraving in a thick layer of lacquer. Then, use printer paper to remove as much of it as possible, switching paper locations frequently to avoid smearing. Finally, touch up the results with printer paper soaked in IPA.

Belt Grinder: Odds and Ends

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.

Belt Grinder: Flat Grinding Attachment

Belt Grinder News! I have finished the flat grinding attachment for my belt grinder. I also have a temporary workrest cut, along with two tooling arms for mounting everything to the grinder. This is very exciting, because it means that the grinder can now be tested under power. (It works great so far!)

The flat grinding attachment will be the primary grinding head for the grinder, and I expect it to be of particular use profiling knives, grinding bevels, and cleaning up castings. Although passingly similar in function to the system on my 2x42 grinder, I expect this head to be much more versatile and much more accurate. Notable features include tilting, and the ability to transition between operating in platen mode and slack grinding mode without using any special tools.

Platen Assembly:

Glass Platen:

The platen provides a flat surface to grind against, and is important for getting good quality knife bevels. As it is designed now, the platen is made out of ATP-5 tooling plate, which has been milled flat, and is connected to its supports by four 1/4-20 flat head screws. Since aluminum is not very abrasion resistant, the platen is faced with a 2'“ x 8” glass plate, which is connected to the main platen with double sided tape and supported from the bottom by a pair of 4-40 socket head cap screws.

That double sided tape is the only really sketchy part of this grinder to date. I believe it will hold, but plan to run the machine in, and grind carefully to start out. If there are issues I will update this text.

Product: USA knife maker 8x2 glass platen.

Machining the initial surfaces. As you might expect, the surface finish on the overhangs left something to be desired.

Machinist’s jacks did solve the surface finish issues, but I over-tightened them, and introduced a 20 thou warp into the part.

This I was able to remove by floating the part on “magic stone” plaster, and facing then flipping the part several times.

Platen Supports:

The platen supports attach the platen to the slack grinding assembly. They feature two 1/4-20 tapped holes for attaching to the platen itself, and a 1/2” slot to allow the platen to be retracted away from the belt when not in use. Although fairly simple in terms of design, these parts were particularly interesting to machine because they are only about 1/8in smaller than the stock in two directions. To ensure sufficient tool access, I cut dovetails 1/16th from the bottom of the part, and held the stock in dovetail jaws. This worked very well, and only added about an hour to the machining time, so I would consider doing it again if appropriate.

Platen Pivot:

From left to right: Tooling Arm, 1/8in washer, platen attachment, 1/16in washer, belleville spring, three 0.005in shims, modified shoulder screw.

I put a lot of time (way more than reasonable) into designing the platen pivot. I wanted something that would be stiff enough to prevent any sort of bending, but also low enough friction to allow for easy adjustment. The traditional approach to this problem seems to be a pair of washers tensioned by a bolt. That works okay, but it means that you are at the mercy of your bolt torque for determining the pivot stiffness. What I settled on instead is a shoulder screw, with a pair of high-load Oilite thrust bushings and a 1400lb Belleville Disc Spring. Four 0.005 disk shims are used to set the tension to 950lbs.

The result is a sturdy pivot, which moves easily and is very resistant to moment loads. With the added bonus that its thrust preload is not impacted by the bolt tightening torque. All this is likely overkill for simply practical purposes, but the result does feel simply marvelous to use.

Tooling Arms:

The 14” tooling arm used for supporting the flat grinding attachment. The opposing sides of each arm are symmetrical, allowing for a wide range of mounting styles.

The grinder uses 1.5” tooling arms too support the grinding and table attachments. In general, these are similar to the arms used by KMG and its clones, but with a few custom twists. In particular, the chamfered rear edge allows for slightly more flexibility out of a given size and the screw-down slot prevent marring on the contact surfaces. The two large holes are 1/2-13 and are spaced by 1.5”, while the smaller holes are 1/4-20 and are spaced by 1.5”. The hole spacing is custom, but the setup is similar enough that I should be able to purchase attachments+arms from a wide range of grinders if I should want to in the future. For the moment, I have made a 14” arm for supporting the flat grinding attachment, and an 18” arm for supporting the tool table.

The arms are cut directly from 1.5” aluminum square stock, and finished on the CNC. As with the body, both arms were then lightly scrubbed with scotch-bright to given them a brushed look.

The two types of side:

These sides mounts the grinding attachments and any large tool tables. The feature through-tapped 1/2-13 holes.

These sides feature 1/4-20 holes for mounting lightweight attachments and my temporary tool rest. The 1/4-20 holes are tapped from both sides to a depth of 3/4”.

Machining Process:

Tooling Rest (likely temporary):

This is a tooling rest for using the grinder in its vertical mode. The design is adapted from a piece of 1/4in aluminum stock I found in the main shop and should be sufficient for freehand beveling and profiling.

The double-sided notch should be useful for profiling the inner corners of knives, and I think the brushed surface should hold up tolerably well, without risking any damage to the items being ground. The one major drawback of the design is not being able to use it when the grinder is horizontal.

This was scrap which I then sawed and filed to shape. As such the fabrication path is not terribly interesting. However, it did provide good filing practice. Pictures of the process can be found below.

Belt Grinder: Structure Build

Summary:

Greetings! This is my build log for the main body of the belt grinder. During this phase of the process, my goal is to complete fabrication of the main structural plates, and then to assemble a mockup of the grinder body. This will let me get a sense for the machine’s ergonomics before setting up the electronics and finalizing the platen design. At this point the grinder is installed and the pivots all work. Next up will be fabricating the platen assembly, and installing the electronics. Until the grinder is up and running we won’t really know how it works, but for now I am very pleased. All of the moving parts turn smoothly, with minimal slop, and the overall structure seems solid. The hold-down lever in particular works quite well (credit to Reeder Grinders for that idea).

I have organized this build log (and pictures) by machine used, rather than part created, since that best matches my actual process for this project. It is also worth noting that both the handle, and tracking plate are completed in these pictures. However, I’ll include their build logs later.

Assembly:

The grinder, fully installed in its temporary home. At this point the structure, and most of the mechanisms are together. Though the tracking adjustment and spring tension will need to be tuned in after the platen build is complete.

All things being equal, the assembly process was remarkably painless. All told the assembly took about 3 hours and, for me, really validates this type of waterjet + drill press construction as a way of building/prototyping large structures. I have included a summary of my process below for anyone looking to build a similar grinder (and for my own reference).

• I started out by using 220 grit sandpaper to give the parts a decorative “brushed” finish. This largely produced the aesthetic I was going for, though on some parts I did have to step down to 80 grit to remove some burrs and nicks. I then washed all the pieces with soap and water, after using IPA to remove the leftover sharpy and marking dye.

• I then clamped the base plate in place above the pedestal ( a lovely Stanley grinder stand we have left over from a dead grinder) and used a hand drill to drill mounting holes in the base, with the corresponding base plate holes as a guide. This worked well, but probably should have been done before the cosmetic touch-ups.

• I then separately assembled the pivot arm, back-plate with pivot plates, and base with pivot legs. I tightened down most of the bolts, but in retrospect ought to have left the back plate bolts somewhat loose and tightened them after assembly.

• With the base and back plate together I then assembled the pivots. This proved tougher than expected, largely because the washers kept falling out. Not a big deal, but if I were doing the build again I would absolutely print a small fixture to hold then in place.

• At this point it was easy to add the tension-arm, vertical and horizontal arm plates, and various knobs. The grinder was then moved to its final spot on the Stanley pedestal and screwed down.

• Getting the motor on took two people (my thanks to Nathan Barton), and might have been easier at an earlier step, though I suspect it would have been “fun” at any point in the process.

Water Jet:

This was my first water jet project, so I was very excited to try it out. All of the structural plates were cut to dimension on the water jet. For the holes, I used the water jet to cut pilot holes and then drilled/tapped/reamed them afterwards with a drill press. The process was virtually painless, and I would certainly consider it in the future for low tolerance / non-cosmetic parts.

The plates were organized into two panels, each 1’ by 4’, to correspond to the 1/2in aluminum stock I purchased for this project. This didn’t leave me quite enough stock to completely build a second grinder, but did provide a nice buffer in case of accidents or for fabricating multiple bases as needed.

Drill Press:

Playing with the main shop’s new laser guided drill press. Turns out the lasers need careful alignment before use, but it’s a neat idea.

Although the water jet is great for cutting profiles, it just doesn’t have the precision for tight tolerance holes, particularly not where they need to act as bearing surfaces of any kind. To provide better hole tolerances I drilled out all of the water-jet holes on the drill press. The 1/4in holes were cut at 1400RPM with standard jobber bits from Mccmaster, and the 1/2in holes were cut at 750RPM using the same type of drills. The 3/4in reamed holes were drilled/reamed at 550rpm. That seemed to be a bit fast for our tooling, but worked well enough in the end.

A special shout-out to the main ME shop for picking up some 3/4in reamers without which this would all have been much more difficult.

The vertical arm plate. I find that writing the intended operations directly on the plates helps cut down on confusion.

All of the pivot plates (and the vertical arm plate) before drilling.

Manual Mill:

The two pivot legs, and two pivot plates, all mount to their respective bases using 1/4-20 holes drilled and tapped into their bottom edges. This will hopefully give me a nice clean interface without taking up too much space or resorting to adhesives. Both parts were designed with a flat reference edge, which I used to align each part in the vise. I then established a reference zero on the (+X, +Y, +Z) corner with an edge-finder and drilled the 4 tap-drill holes on each part. The threads were cut by hand with the part still on the machine.

Story: While spotting my final set of holes the HSS drill snapped off in my part. I was subsequently able to simply cut through the remains of the bit using a 1/4in carbide endmill. I consider this sequence of events to be a lesson in both the hardness of carbide, and the importance of purchasing quality tools.

Using one part as a crude 90 degree reference for another. The copper block is to ensure only one of the two parts is clamped when tightening the vise.

3D printer:

Although not strictly required for a test fit-up, I decided to 3D print a few of the fiddlier tension and hold-down components to get a better sense for how everything will go together. These parts need to last through a few fit-ups, but shouldn’t see more than 3-4 hours of actual grinding use. With that in mind, I printed them with my standard settings (20% infill, .6mm walls, .2mm layer height) and all of the threaded holes enlarged to take heat set inserts.

Belt Grinder: Fabrication Plan

Summary:

This project has a lot of separate parts that need to be machined or otherwise fabricated. This document is a place for me to keep track of what I have made, and what I still need to make.

Note: This is a living document, I will keep it up to date as the process proceeds.

Key:

B = Blocked.

C = Completed.

I = Incomplete Design.

P = Printed.

Main Grinder:

The main body and mounting hardware for the grinder. This

• Base (1): C

• Legs (2): C

• Back Plate (1): C

• Tension Plate (1): C

• Hold Down Plate (1): C

• Tracking Clamps (2): C

• Tracking Blocks (2): C

• Spring Guides (1+1): P

• Hold Down Pivot Block (1): P

• Large Arm Plate (1): C

• Forward Handle (1): C

• Pivot Plates (2): C

• Tracking Plate (1): C

• Small Arm Plates (2 + 1): C

Platen attachment: (Fabrication In Progress)

The primary grinding attachment, used for general contouring, handle work, and bevel grinding. Once this is complete the grinder will be usable.

• Arm: Fabricate.

• Slack Plate: Tap remaining holes, sand.

• Platen Mounts: C

• Platen: Fix warping, Glue.

• Grind Table: Cut to rough shape, CAD.

• Machine Spacers: Fabricate.

Main Electronics: (Design Ongoing)

A secondary grinding attachment used for complex profiling. I have not yet decided to begin designing/building this attachment

• Wiring: Purchase wires, purchase glands, run wires.

• Testing: power on, configure.

• Modify support plate: design, cad, cam, fabricate.

• Modify front face: source switches, design, cad, cam, fabricate.

”~~~~~~~~AT THIS POINT PROJECT “COMPLETED”~~~~~~~~

Small Wheel Attachment: (Design Ongoing)

A secondary grinding attachment used for complex profiling. I have not yet decided to begin designing/building this attachment.

• Arm: I

• Outer Plates (1+1): I

• Inner Block (1): I

• Wheels (N): (buy?) I

Variable Work surface: (Design Ongoing)

A more robust, accurate grinding platform.

Belt Grinder: Project Goals

What is this?: 

When I start a new design project I always record my general design goals for the project before starting out. I find this helps keep me on track and cuts down on unnecessary feature creep. This is mostly recorded here for my own benefit during future design revisions, but may 

Overview: 

This is a medium length (40 hour) project intended to expand my repretwar of knife making tools and give me a bit of machinery fabrication experience before tackling something CNC.  A belt grinder is a device used to remove metal, or other materials, from a part through the use of an abrasive belt. This particular grinder is being designed with knife making in mind, and as such will use the 2" by 72" belts standard to that pursuit. 

This unit will be designed to live in the Caltech Student Shop during the remainder of my time here, though I will likely take it with me when I leave. Since my future housing is not known, power and space requirements will be dictated by what is available in the Student Shop.

Learning Objectives: 

• Become comfortable using the Water Jet.

• Become comfortable using the Haas TM1.

• Get experience designing belt tracking systems.

• Get experience using solid works modal analysis.

• Get experience using GD&T.

Product Objectives: 

My product objectives are broken down into three categories as follows. Items in category "need" are required for a design to be worth considering. Failing to fully realize this category is a no-go check for the project. Items in the "want" category are things I feel dramatically improve the base functionality of the grinder. The goal is to incorporate all of these features, though some may be ignored if need be. Items in the "dream" category are things I feel would expand the functionality of the grinder. The goal is to incorporate a few of these, though likely not the majority.

Need:

·         1.0hp motor.

·         Interchangeable attachments.

·         Square workpiece supports.

·         Adjustable tracking.

·         2x72

·         Platen, slack, and small wheel grinding.

·         120v

Want: 

·         1.5hp motor.

·         Adjustable speed motor.

·         Self-contained unit.

·         Interchangeable workpiece plates. 

·         Identical platen edges.

·         Direct drive. 

Dream:

·         Tilting grinder.

·         Adjustable workpiece plates.

·         Portable.

·         Speed readout.

·         One handed belt change.

·         Mist coolant.

Project Completed When: 

• The grinder unit is fabricated, calibrated, and tested.

• Either a platen or large wheel attachment has been installed.

• Fabrication and assembly plans have been compiled into a cohesive document.