Heavy Duty Engraving

Following are some basic theories and considerations when engraving in materials harder than normal plastic (stainless, brass, aluminum etc.).

Material placement and hold down

Typically, for this type of engraving, you will NOT be using a nose cone to control your depth of cut but will employ the use of 'Manual Cutter Set at Start', 'Multiple Pass Setup' and 'Free Blade Engraving' (a term that I use to describe non-nose cone engraving). Since the depth of cut will solely depend upon a fixed descent of the cutter (Z-Axis) into the material and across the entire surface of the material, it is very important to place the material on the 'flattest' part of the engraving surface, and restrain it from any type of movement.

The 'Flattest' part of the engraving surface

On moving T-Slot tables (13x13's, 16x25's 12x12's, 12x24's and 16x24's), the flattest portion of the engraving surface can usually be found in between the bearing mounts found under the T-Slot engraving surface. This places the material away from the usual 'home position' and will require some new offset values for a point of origin.  Click here to see more on setting a temporary home position.

Restraining the engraving material (clamps, vices etc.)

This type of engraving far exceeds the restraining ability of engravers tape or masking tape. It is strongly recommended to use either a clamp or vice which will offer both a rigid, consistent mounting location, and ease of use (especially if you are engraving mass quantities). You want to be able to install and remove material as efficiently as possible without sacrificing flatness and rigidity. Lack of flatness will yield inconsistent depth, and a loosely held piece of material will yield poor engraving quality, as well as shorten your cutter life.

Custom Jigs

For highly repetitive work, you may want to consider a custom jig designed specifically for that sized plate or job. Some extra time spent creating a simple means for installing and removing the material can make the labor time much more efficient. A good, efficient jig should allow for quick yet accurate placement of material, with minimal effort.

Cutters, Cutting Fluids, and Spindles

This type of engraving, for obvious reasons, is very tough on cutters (as opposed to standard plastic engraving). Whatever style cutter you end up using, you should plan on having many duplicates for replacement (broken cutters) and for re-sharpening. If this ends up being a major part of your business, you may want to consider purchasing your own cutter sharpener.

As far as cutters, it is recommended that standard engraving cutters (designed for cutting metals : MTL), and 'machine shop' style end mills (specifically, double-ended, double fluted end mills) be used.  As far as engraving quality and ease of use, the end mills are far superior.

It is also recommended that a cutting fluid be used.  This will extend the life of your cutters by lubricating the cutting surface and help to cool them as well. You will also find that this will help produce a smoother finish on the cut.

A collet spindle is also a must for this type of engraving. Standard top load spindles do not offer the necessary support of the cutter down at the bottom of the spindle and will allow the cutter to 'chatter' under heavy engraving loads. This will produce poor engraving quality, reduce the life of your cutters, possibly breaking them. The 'end mill' style cutters mentioned above typically come in short lengths (as short as 2 inches), requiring a collet spindle for their use.

Locking Out the Z-Axis Spring

Since stainless is obviously a lot harder than plastic, it will require a lot more pressure to penetrate the surface. To get maximum pressure and a 'direct drive' relationship of the Z-Axis stepper motor to the spindle, it will be necessary to 'lock out' the spring on the Z-Axis assembly. Consult your table manual for instructions for your particular table on how to do this.

Software Setup

Modifications in the software are basically made to slow down the operation of the engraver. The variables addressed here are found in two separate dialogs: Engraver Setup, and Engraving Software Setup.

Engraving Software Setup  

In the Xenetech software, select Page | Engraving Table Defaults...  There are two variables in this dialog that lend themselves for adjustment:

Traversing Speed Index

Traversing controls the XY directional speed when the cutter is in the up position (not down on the material engraving, but traveling from character to character, or from the home position to the first character, etc.) Typical values for Traversing range in between 15 to 25. You may want to slow the Traversing by increasing the value to 50 (remember, higher speed values in the Xenetech software yield slower speeds). Slowing down the Traversing simply allows you to 'keep up' with lubricating the cutter.

Deceleration Index

Deceleration controls how much start-up or low end power the stepper motors use to move their respective axes (X, Y, and Z). Since you are engraving in harder material, it may require more power to move the cutter through the material (as compared to plastic). Typical values for Deceleration are in between 70 and 110. For heavy duty engraving, raise this value to at least 175.

Engraver Setup

In Xenetech select File | To Engraver...

There are four variables in this dialog that lend themselves for adjustment:

Z Stroke

Controls the amount of 'lift' of the cutter in between characters. Just make sure to have a large enough value preventing the cutter from dragging through the material in between characters. Typical values range in between .062 and .125 inches. As a general rule, try to set your Z Stroke to at least twice the final depth of cut. For example, if you are cutting completely through 1/8 inch material, set your Z Stroke to 1/4 inch (0.25). This will ensure that your cutter will not drag through the material when picking up to move to the next character, line etc.

Z-Delay

The Z Delay value represents a time constant delay controlling the time of the cutter coming down to the table surface verses the time that the X and Y axis begin to move. This value is important in giving the cutter time to fully penetrate the material to the desired depth before making a lateral movement either in the X or Y direction. For plastic engraving, a value of 25-40 is nominal for average depth engraving (7-15 thousandths). You may need to raise this value to allow the cutter to fully penetrate into harder materials. Try 75 to 100.

Z-Down Speed

Z Down Speed represents the velocity at which the Z Axis travels in its down stroke. For all practical purposes a value between 6 and 12 is recommended for tables having a Z-Axis with a resolution of 6400 steps per inch (recent Western tables). Newer Xenetech engravers (13x13's 16x25's, 25x25's and 25x50's) should use a value of at least 35. For harder materials, or deep engraving, slowing the Z Down Speed is recommended, by increasing the value of the Z Down Speed. Start at a value of 75. The Z Feed knob on the Pendant can also help you fine tune the Z Down Speed.

XY Speed

X-Y Speed describes the actual engraving speed. The engraving speed is defined as the X-Y directional speed at the cutter with the cutter in the down position (on the material, as opposed to traversing speed - cutter in the up position). You will want to slow this down to prevent breaking off cutters as well as maintain a quality cut. Try running it around 100. This value will vary dependent upon the material, the depth of cut, the sharpness and condition of your cutter, etc. As you can see, there are a lot of variables involved here. In you particular application, you may be able to increase the X-Y Speed, or possible may need to decrease it.

Multiple Pass Setup (found under the Misc menu)

In Xenetech select Misc | Multiple Pass Setup...

For a cleaner cut and for less abuse both to your cutters and engraver, it is recommended to use multiple passes to acquire your final depth rather than in one pass. On stainless you can typically engrave 5 to 10 thousandths of an inch deep safely and acquire a clean cut. A final clean up pass also helps to clean up burrs generated by cutting deeper on the initial cuts. Clean up passes typically are no more than 1 or 2 thousandths deeper on the final pass. So for a desired depth of 12 thousandths (.012), set pass number one to .005, pass number two to .011 and pass number three (clean up pass) to .012.

Manual Cutter Set at Start

Since you will not be using a nose cone to control your depth, you will NOT have the luxury of using Full Automatic Cutter Set (and of course the Proximity Sensor). Manual Cutter Set at Start is typically used in this situation to reference the surface of the material so that the passes set above in multiple pass have a starting place. So when performing the manual cutter set, simply bring the cutter down to the surface of the material. There are two approaches for determining whether or not you have reached the surface. The first is to have the spindle motor running so that the cutter is rotating. Bringing the cutter down slowly, you will see a small amount a chips 'fly' once the cutter makes contact with the surface of the material. The second requires a thin piece of paper and have the spindle motor not running. Slowly bring the cutter down while holding the paper on the material surface under the cutter. Move the paper around slightly awaiting pressure from the down coming cutter, indicating you have reached the surface.

Spindle Motor Speed (rotational speed of the cutter)

This is relative to cutter size, engraving depth, XY Speed, the type of cutter, and the sharpness of the cutter. As you can see, there are a lot of variables. Too slow of a speed setting can increase your chances of damaging or breaking off the tip of the cutter, as well as affect the engraving quality. Too fast of a speed setting can actually cause the engraving material to 'fuse' onto the tip of the cutter. This effectively creates a very dull cutter resulting in a rough 'gummy' looking cut in the material. Start your spindle motor speed around 5 or 6 on the motor speed control and listen to the engraver as it cuts the material. Adjust the speed up and down (in small amounts) while listening to the engraver. Attempt to find a setting that 'sounds' as if the engraver is not having to struggle or labor through its cut. This takes a little practise through trial and error, so don't get discouraged if it doesn't seem obvious at first.