Hollow Grinding

From Shave Library
Jump to: navigation, search

Before beginning any work in the shop, be sure that you have taken all safety precautions and have the necessary protective equipment. This includes, but is not limited to: Eye protection, proper attire, and a respirator.

This guide is intended to give an introduction to hollow grinding a razor blank. For this example, we will assume that we are starting with a blank that has already been profiled as shown in the graphics. Also, You should start with a blank that has been annealed prior to grinding.

Marking the center[edit | edit source]

The first step is marking the center of the blank. There are many ways to do this with various layout fluids, marking media, gauges and tricks, but the mark must be accurate. The center line will be your guide for everything, and should be scribed around the entire blank (this will help with shaping your tang).

One way to make a good center mark is to find a drill bit with the same diameter as the thickness of your stock. Once you have the correct bit, lay the bit and the blank on a level surface and roll the point of the bit along your blank. The point of the bit will be exactly in the center of the stock. Below is an animation that may be helpfull for illustration.


Making the initial grind[edit | edit source]

After the blank has been marked, the initial grind can be made. At this point, your grinder should be equipped with a fresh coarse belt (40 grit or so) in order to remove stock quickly.

The blank should be held firmly (but don't get carried away) with the edge pointing up toward the path of the grinding belt. In other words, if the belt is rotating down toward the floor, the edge should be pointed in the opposite direction.

You may start your grind from heel to toe, or from the middle and work out, but you will need to make sure that you grind the entire edge evenly. At first this may be difficult, but you'll be able to see where you may need to change your grinding form by constantly checking your progress on the blank under a good light. Below is a graphic demonstrating the basic approach.

Here is how the blank is presented to the contact wheel Slide1.jpg

here is an example of the grinding motion Initialgrind.gif

Be careful to keep the blade in the same relative position on the wheel throughout your lateral passes. If you allow the blank to move irregularly upward or downward as you move from side to side your grind will be uneven. *If you are using wheels of differing diameters throughout your process, up and down motion may be helpful for blending the grinding marks for each wheel*

Once you have made an even hollow groove across the entire edge, you can start moving the grind up the spine.

Moving the grind up the spine[edit | edit source]

Once the initial hollow groove from the first cut is established, continue to grind by following the groove from your initial cut, and work the blank upward on the wheel as you continue to grind back and forth (really just hint the razor upward with a bit of pressure on the spine area if that makes sense). Movingupgrind.jpg

Again, follow the groove, working the razor up the wheel with a hint of pressure on the spine in order to hollow out the blade as high up as needed. After completing this with the course belt, refine the grind with progressively higher grit belts until you reach the desired finish prior to heat treating. Once you have finished this, you have completed one side of your rough grind.

Repeat on the other side[edit | edit source]

At this point, you will flip the blank and repeat the process until both sides are roughly hollowed out. Bothsidesgrind.jpg

Be sure to leave the edge thick so that your blank doesn't warp from the stresses of heat treating. Somewhere between 1/16" and 1/8" seems to be a good thickness to stop at.

considerations[edit | edit source]

Be sure to check your progress frequently under good lighting, this will help you identify and correct your mistakes. Some have the tendency to favor one area of the blade as shown here (favoring the middle area) Evengrind.jpg

Below is an example of how the grinding motion may be for a smiling blade blank. For this type of razor, you may consider using a thinner contact wheel (thinner than the 2" standard width).  Smilegif.gif

Belt Selection

You may find that using such a coarse belt at first doesn't suit you as well. Try starting with a 80 grit for the hollow grinding to reduce the deep scratches that have to be worked out.

Contact Wheel Selection

Most wheels are flat and 2" wide, that gives more contact with the steel at one time but also requires us to compensate by moving the blade laterally to even up the hollow grind.

There are 3 other options
A. Use a narrower wheel... thisis the best option for a blade with a
curved spine/edge
( smiling blade shape)
B. Use a wheel that is crowned in the center in profile
C. Use a wheel that is half round in profile

A 3" wide flat faced wheel is of no use.... it would leave deep scratch marks because the blade is stationary. The blade must be moved to blend out the scratch pattern from the abrasive belt.

Speed of Belt

To be clear, this is about the speed of the BELT not the drive wheel or motor. For profiling/shaping the razor blank a high speed is desirable. Most of the grinders come with a 4" drive wheel ( not the contact wheel). assuming a 1750 rpm motor that will drive the belt at 4 x 3.146 = 12.584"/12 = 1 ft per revolution or 1750 surface feet per minute of belt speed. That is a good speed for grinding the hollow of the blade. But for profiling you need to double that speed unless you have a lot of patience. Finish grinding is best done at 1/2 that speed or even less ( less is better) such as 400 sfpm. larger drive wheels may not be best for hollowing. For example, a 10" drive wheel is great for profiling, but cannot really be used for hollow grinding or finish grinding. The steel simply gets hot so very fast.

contributions[edit | edit source]

thanks to all who contributed to this, especially on this thread at SRP https://straightrazorpalace.com/forge/50486-grinding-thoughts.html

Please continue to add any information as appropriate, Thanks again.