| Wednesday, June 22nd, 2011 | Published in: Tech Tips & Tricks |
In 2001, GRS introduced a new general purpose handpiece: the Model 901 (#004-901). It offers a wide range of power for engravers and jewelers in a compact size and ergonomic shape. The popularity of this handpiece is due to its versatility, ruggedness, and easy serviceability.
In 2007, GRS introduced Airtact Control System, which gives the user a wide choice of handpiece control options including palm push actuation. To use any 901 handpiece with Airtact, the user simply exchanges the standard handpiece knob with an Airtact-enabled version. These special knobs interface with the Airtact Control System for complete hand control. There are presently two ways to get an Airtact Control System. The #004-935 is a compact, stand-alone Airtact Control unit that adds Airtact to any GraverMax, GraverMach, GraverMate or GraverSmith. The second way is the #004-965 GraverMach AT which has a full Airtact Control System built in. The GraverMach AT also includes instant switching between hand and foot control that is unmatched in versatility and convenience.
The purpose of these instructions is to show the user how to optimize the 901 handpiece for different applications, especially fine hand engraving and stone setting. This information is useful no matter how the user controls the 901…by foot or hand. For Airtact hand control users, this tutorial also includes references to significant improvements in Airtact that provide finer control of handpiece power at all levels. Additionally, there are special “tricks” and fine-tuning recommendations that apply specifically to the 901 handpiece, especially when using Airtact for palm push control.
901 Handpiece Configurations and Options
901 Handpiece Spring
All new 901 handpieces include two different springs:
- LONG spring: Factory installed in all 901 handpieces; gives MAXIMUM power.
- SHORT spring: Included with 901 but not factory installed. gives FINEST control.
When selecting either the long or short spring, note that jewelers and stone setters generally prefer the LONG spring for maximum power. Many engravers prefer the SHORT spring, which provides a softer start and finer control.
How to identify the spring:
- 901 LONG Spring (#004-411-V2) is 1.33 inches (33.8mm) long X 0.40” (10.2mm) outside diameter.
- 901 SHORT Spring (#004-430) is 1.11 inches (28.2mm) long X 0.40” (10.2mm) outside diameter.
901 users also have a barrel length option described later in this tutorial. When choosing which spring to use, keep in mind that the length of barrel can also be a factor. If you choose the LONG spring, it’s normally recommended to use only the long barrel. If you choose the SHORT spring, both the long and short 901 barrels will both work
Comments on Spring Length and Handpiece Operation
The long spring generates a longer piston stroke for greater impact power. The long spring requires a higher air pressure setting than the short spring (about 6 PSI). If you don’t adjust the air pressure setting to properly match the particular spring installed, the handpiece WILL NOT perform correctly. For example, if you change from the long spring (MAXIMUM POWER) to the short spring (FINEST CONTROL) but do not adjust the air pressure setting, the handpiece will not operate with the FINEST CONTROL available. Adjusting to the proper air pressure setting will allow the best operation of the handpiece with the installed spring.
901 Handpiece Piston
From 2001 to mid-2009, the piston was made from solid heat-treated stainless steel with a thin external coating for lubricity. In mid-2009, a new piston made with a special self-lubricated composite outside, and a tungsten carbide center was introduced. This new piston offers even finer control with cleaner operation for virtually zero wear. Earlier 901 handpieces can be retrofitted with this new piston; if you do, it is recommended to install new springs as well. Also, there is a special tutorial on handpiece cleaning that is very useful if you are replacing the piston and spring with new parts; here is the link: http://www.grstools.com/PDF/LIT-324_HPclean.pdf
How to identify the 901 piston:
- 901 ORIGINAL Piston (#004-406-V2) has four small grooves in the outside diameter and a dark gray coating that may have worn off substantially with use.
- 901 NEW Piston (#004-406-V3) is smooth on the outside (no grooves) with a fairly uniform dark gray color. The outside is solid composite (plastic) material; the inside is tungsten carbide.
901 Handpiece Barrels
When Airtact hand control was introduced in 2007, it required a different handpiece knob than the standard one. The Airtact version knob is longer to accommodate the rubber palm element and control air connection. If the Standard 901 barrel is used with the Airtact 901 knob, the extra handpiece length may be noticeable to some users. To shorten the Airtact 901, an optional short barrel can be installed that makes the 901 Airtact handpiece the same length at the original Standard 901 handpiece. Thus, there are now two 901 handpiece barrels: the standard (long) barrel and the short barrel. The difference in length is about .20 inches (5.1mm). NOTE: If the short barrel is used, the short spring is usually recommended to avoid impacting the inside of the knob with the back of the piston.
How to identify the barrel:
Airtact Hand Control for 901 Handpiece
All 901 handpieces are easily adapted to hand control. There are two types of hand control: palm and thumb / finger. Palm control is the most popular and requires a special Airtact knob to replace the Standard knob. If the handpiece was ordered as an Airtact (AT) version, it already has this special Airtact knob. If not, the Airtact knob must be installed.
Understanding 901 Airtact Knobs
Airtact works using a second air circuit called the Control Air. (The main air circuit is the Power Air, which is pulsed to move the handpiece piston back and forth). The Control Air is a special low pressure “air leak”. Plugging this “air leak” shifts a pneumatic valve inside the Airtact system which varies the Power Air in proportion to how much this “air leak” is stopped. Blocking the “air leak” entirely delivers full power to the handpiece. While the Airtact system is more sophisticated than this simplified explanation, it helps the user understand how it works.
When the user wants to control power using the palm, a special handpiece knob with a Palm Touch Element is used that has a Control Air connection on the back of the knob. On the upper back of that special knob is a small vent hole that allows the Airtact Control Air to “leak”. A contoured rubber cover, also called a Palm Pad, is installed on the rear of the knob to add comfort and fine control for the user.
For the 901 handpiece, there have been two Airtact knob designs. The first was larger in diameter and more mushroom-shaped. This version was standard for about two years (2007-2008). The second and current knob version is smaller in diameter and more rounded in shape. This second knob design, based on Airtact user feedback, allows users better hand control and more comfort than the first design.
How to identify 901 Airtact Knobs:
- 901 First Version Knob: outside diameter is approximately 1.31” (33.3mm)
NOTE: Stainless steel knobs are shown; aluminum knobs are the same size and shape, but black in color.
- 901 Second Version Airtact Knob: outside diameter is approximately 1.18” (30.0mm
Airtact Rubber Palm Pads
Airtact knobs have a special rubber cover, called a Palm Pad, which provides an important function. The top center part of each Palm Pad has a thick contoured rubber flap that covers the knob’s Airtact vent hole. When the user pushes on this flap with their palm, it begins restricting the Control Air flow to vary handpiece power. There are several styles of Palm Pads now available, but the newest ones are Type E. These latest pads come in three sensitivity levels: #6, #8, and #10. The lower the number, the more responsive the handpiece becomes (less hand force required). Most users should try #8 first and switch to #6 if they want to use less hand force, or #10 if they want to use even more. Type E pads work on any Airtact knob and are especially designed to complement the second version of 901 Airtact knobs.
• Type E Palm Pads are the latest design with larger, easier-to-use control flaps
• Older Palm Pad
Note: There are other (older) Palm Pad designs not shown above. Type E is recommended and preferred by most Airtact users.
Special Tips for Customizing Airtact Hand Control
Once a user understands Airtact, it is easy to customize handpiece response. Keep in mind working preferences differ widely; some people prefer a light touch while others want to push more by hand. In general, most Airtact users will want a lighter touch handpiece (that is, less hand force to actuate) as they gain experience. Keep this in mind when considering the advice of others. The information that follows will help any user match handpiece response to their requirements. The first step should be to determine which particular Palm Pad fits best. Then, by forming or bending the control flap one way or the other, most users will create the feel they prefer. If more fine tuning is desired (or for those who enjoy experimenting) there are more steps to consider: modifying the Airtact knob vent hole, and texturing the underside of the rubber control flap.
“Forming” the Rubber Control Flap
The hinged rubber control flap on the top of the Palm Pad transfers hand force into handpiece power. It does this by covering up a small air vent hole in the rear of the Airtact handpiece knob. Forming or bending the rubber control flap one way (concave), increases the required hand force; bending the other way (convex) decreases the hand force.
This photo shows how to increase the hand force required to operate the handpiece by bending the control flap into a more concave shape. Bending the flap this direction keeps the flap from sealing off the Airtact knob hole until more hand force is applied.
In this photo, the flap is bent to decrease the hand force required. Bending the flap in a more convex shape seals the Airtact knob hole with less force applied.
Modifying the Airtact Knob Vent Hole Shape
Airtact knobs have a round vent hole that is approximately 0.050” (1.3mm) in diameter. This round hole works well for most applications. Some engravers may want finer, softer starts in their cuts for fine shading, etc. By slightly modifying the vent hole geometry with a graver, improvement in fine control is possible.
Step 1: Start a graver cut about 0.20” (0,5mm) above the top edge of the hole itself. A round graver such as a standard #52 round or a wide point graver like a 120° point will work for this.
Step 2: Cut toward the vent hole going progressively deeper until the graver gently breaks through the wall of the hole. Refer to the photo to see the size of the graver cut width compared to the size of the vent hole. If you want to be conservative, make a smaller cut and see how it affects the Airtact handpiece control overall. You can always make it deeper and wider if desired later.
Step 3: Lightly debur and slightly polish the edges of the graver cut. Do NOT overdo the deburring or polishing, which could change the contour of the knob too much.
"Brush Texturing" the Rubber Control Flap
Another modification that some Airtact users like is to apply a slight texture to the underneath side (the surface that seals the vent hole) of the Palm Pad rubber control flap. This is done with a small, soft rotary brush used with a rotary handpiece such as a micro-motor (NSK) or flex-shaft (Foredom) system. This light texture softens the start-up but requires a little more hand pressure to control power. With this modification, start with a low force style Palm Pad (such as the #6) and be very careful to run the brush at relatively slow RPM. It is quite easy to remove too much rubber by turning the brush too fast or using too much pressure.
Cautions: make sure you use a soft brush, run it fairly slowly and rotate the brush in the direction that pulls the rubber flap away from the pad, not pushing it toward the center of the pad. If you texture the flap too much, you may change its shape enough to make the hand force required higher than you want.
Summary
901 Handpiece use with or without Airtact For Engravers who prefer fine control over maximum power:
- Use short 901 barrel
- Use short 901 spring
- Make sure piston is the new version
For Jewelers & Stone Setters (or anyone who prefers to maximum power):
- Use long 901 barrel
- Use long 901 spring
For All 901 Users:
- Keep handpiece piston and bore clean; piston should drop freely in and out of the barrel using only its own weight. A clean handpiece will have both greater power and finer control.
- If the handpiece needs to be deep cleaned, following the instructions on this link: http://www.grstools.com/PDF/LIT-324_HPclean.pdf
For 901 Airtact Hand Control (Palm) Users:
- Try different Palm Pads and select the one that best fits the user’s working style.
- Form/bend the rubber flap to make hand (palm) force more or less as desired.
- Modify the Airtact vent hole with the special graver cut
- Lightly brush texture the rubber control flap
- Select the best barrel and spring for your application (see above).
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