Chemical bond
- Joint can be as strong as the soft material itself
- Needs a resin pair known to bond
- Sensitive to core temperature and to surface condition
Molded part guide: tool handles
Injection Molded Tool Handles
A soft grip is the part of a tool that a user actually judges. It has to stay firmly attached to the rigid handle underneath through years of squeezing, twisting, dropping, and contact with whatever the tool works in. When grips fail it is almost always at an edge, and almost always because of the interface, not the material.
Two layers
The grip is only as good as its interface
Power tool grips, hand tool grips, garden tool grips, and handle overmolds.
A grip is a soft layer shot over a rigid core. The rigid part, usually nylon, polypropylene, or a glass filled grade, gives the handle its strength. The soft layer, usually a thermoplastic elastomer, gives grip, cushioning, and the feel of the tool. The two are separate materials, so something has to hold them together.
Two things can. Some resin pairs bond chemically at the interface when the soft layer is shot onto the hot core, giving a joint that is as strong as the soft material itself. Where a pair does not bond well, the design adds mechanical locks: holes the soft material flows through, grooves it keys into, and undercuts it wraps around. Most production grips use both.
Failures start at edges. An edge of soft material lying flat on the rigid surface is a place a fingernail, a tool, or a pocket can catch and lift, and once a lift starts it travels. Recessing the edge into a step in the rigid part, so the soft layer sits in a shallow trench with its edge protected, removes almost all of these failures.
Then the working environment finishes the job. Fuel, cutting oil, solvent, and sweat all swell some soft grades, making the grip go tacky, slippery, or loose. A grade chosen for the actual fluids the tool meets keeps its feel, and a grip section that is even keeps it from tearing where it is thinnest.
Features
Grip features and what each one is for
Interface, edges, and section decide how long a grip lasts.
| Feature | Purpose | Design note |
|---|---|---|
| Soft grip layer | Grip, feel, and cushioning | Even section so it does not tear where thin |
| Rigid core | Handle strength | Shaped to support the grip along its length |
| Mechanical locks | Hold the layers together | Holes and grooves the soft material flows through |
| Recessed edges | Stop peeling | Soft edge sits in a step in the rigid part |
| Texture on the grip | Wet and gloved grip | Molded in, so it cannot wear off |
Interface
Grips fail at the edge, not in the middle
An exposed soft edge is an invitation to lift, and lifting spreads.
- An edge lying flat on the hard surface can be caught and lifted
- Once a lift starts it travels along the whole edge
- Recessing the edge into a step in the rigid part protects it
- Holes and grooves let the soft material key into the core as well as bond to it
Attachment
Chemical bond or mechanical lock
Most production grips use both, but one usually leads.
Mechanical lock
- Works even where a pair does not bond
- Holds if the bond is weakened by fluids or heat
- Needs holes, grooves, and undercuts in the core
Drawing
What to send with a tool handle
The fluids and the grip force decide the soft grade.
Handle CAD showing the rigid core and the grip area
Grip hardness and feel you want
Fluids the tool will meet, such as fuel, oil, or solvent
Temperature range and sunlight exposure
Vibration levels, if the tool is powered
Expected annual volume
Keep reading
Related guides
Handle shells, soft resins, and the second shot that covers them.
Handles
Rigid handle shells and stiffening.
HandlesKnobs
Grip, feel, and shaft fit.
KnobsSurgical instrument handles
Handles around a metal shank.
Surgical instrument handlesSafety guards
Guards on the same tools.
Safety guardsOvermolding
Shooting soft over rigid.
OvermoldingTPE
The usual soft grip resin.
TPEDelamination
Layers that separate.
DelaminationConsumer products
How we support consumer programs.
Consumer productsMolded parts hub
Every part-type guide, grouped by family.
Molded parts hubFAQ
Questions about molded tool handles
Why do our grips peel at the edge?
An exposed soft edge was caught and lifted, and the lift travelled. Recessing the edge into a step in the rigid part, so it sits in a shallow trench, stops nearly all of these. A simple peel test at the edge of the grip, on early parts, shows whether the interface is doing its job.
Do the two materials really bond?
Some pairs bond chemically and very well. Others barely bond at all, so the design leans on holes, grooves, and undercuts that the soft material flows through and keys into. Where a pair bonds poorly, holes through the core give the soft material a path to lock through rather than only onto.
Why did the grip go tacky after use?
A fluid in the working environment swelled the soft grade. Fuel, cutting oil, and some solvents do this. A grade chosen against those specific fluids keeps its feel. Soaking a finished grip in the working fluid for a few days shows the swelling long before a customer does.
Can a grip be added to an existing handle?
Yes. The rigid handle is molded first, then placed into a second tool where the soft layer is shot over it. The rigid part usually needs locking features added.
Next step
Quote a handle with its grip
Upload the handle and mark the grip area. DFM feedback covers the resin pair, mechanical locks, edge protection, and grip section.