Davenport Machine

Davenport Machine

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Daven Screw Products

General Info

The Davenport 5 spindle automatic screw machine was originally built in 1909. It is the one screw machine that has had the least design changes made to it since its' construction. This means that parts made for new machines today are able to fit machines as old as 70 years old. Because of this, it is one of the least expensive screw machines to maintain.

The machine is designed to manufacture parts at rates from 120-4500 pieces per hour. Hourly rates on the Davenport range from $25-70/hr. depending on the shop doing the work and complexity of the job.

Lead times in most shops ranges from 4 to 12 weeks normally, depending on the economy.

Most parts are made complete with no secondary operations required, thus reducing the overall cost of the part.

If you are doing business with a Davenport shop, you should expect clean parts with no scratches, marks or chatter. They should come free of all burrs and have the appropriate chamfers, whether called out on the print or not. Any Davenport shop should chamfer the parts unless a sharp corner is called out on the print.

Capabilities of the Davenport

The Davenport Machine is designed for high volume low cost production. Quantities produced range from 1,000 to millions of pieces, though most quantities run are between 10,000 and 1,000,000 pieces.

Davenport machinists love to run parts with tolerances of ±.005 on lengths and ±.003 on diameters. The machines are capable of manufacturing in tolerances of ±.001 on length and ±.0003 on diameters and with a microfinish of 16 RMS and very few machinists are capable of making a Davenport hold these tolerances.

Length: up to 5 inches, but usually up to 3 inches

Diameters: up to 7/8 (.875) round and 3/4 hex, but usually 3/4 (.750) round and 5/8 hex.

Common special operations done on a Davenport are:

	The Davenport is specially suited to make threaded parts, internal and external
	Slots ( for a screwdriver or expandable part)
	Flats (External, sometimes one or two flats and sometimes a hex or square)
	Broaching (for allen wrenches, splines, etc.)
	Cross drilling and cross tapping
	Deburring while parting off is done on most parts (no cut-off nib or burrs)
	When a thru hole is made, a deburring tool is used called a back drill
	Drilling in the both ends of the part is commonplace
	Recessing (a groove on the inner diameter of a part)
	Trepan ( a groove in the end of a part)
	Knurling ( a spline-like mark on the outer diameter or end of the part that can be a straight, diagonal or diamond shape that provides a good friction grip) commonly seen on thumb screws

How a Davenport works

The basics are that you put bar stock into one end of the machine, each work station cuts the bar down to the part you have ordered and the part is dropped into a basket completed.

This requires a lot of tooling and set-up work. Once a machine is set-up, the machine will automatically produce the parts. The machine must be monitored constantly to ensure that it is making parts to specifications.

A more detailed explanation

The machine has 5 work spindles that each have a collet to hold the bar stock and a feeder to feed the bar stock. Five bars that are 12 ft. long are loaded into the machine to be cut into the parts you have ordered.

Work is performed in each of the 5 positions of the machine, each at the same time. It all works like an assembly line. In each station of the machine a different operation is performed on the part to cut it into the part you have ordered. The work spindles move from one tool to the next until the part is completed and then the process begins all over again.

A basic job would work something like this:

It all begins with a 12 foot long bar of material.........

The First Station

	From the end in the first position, a center drill starts the hole and leaves a lead in chamfer for the next drills and tap while a special made facing tool cuts on the end of the part setting the length of the part to specs.
	From the side, a form tool (with the basic contour of the part ground into it) cuts a rough form shape of the part.

The Second Station

	From the end, the part is drilled more than half of the depth required by the print.
	From the side, another form tool (with the shape of a finished part) cuts on the outer diameter until the part is within .002 to .005 inches of the print specs.

The Third Station

	From the end, the part is drilled to the depth and diameter called out on the print.
	From the side, a shaving tool (with the perfect form of a finished part) is used to shave off the .002 to .005 inches left by the previous form to size the part to the precise outer diameter dimensions called out on the print.

The fourth station

	From the end, the part is tapped with the thread that is called out on the print to the depth that is specified.
	From the side, a knurling tool presses a knurling form tool against the part as it turns to give a grip for the part as specified by the print.

The Fifth Station

	From the end, the Pick-off spindle and collet approach the part and clamp on the part while the part is being cut-off from the bar stock. When the operation is complete, the pick-off will release the part over a chute that conveys the part into a basket.
	From the side, a cut-off tool cuts a radius on the back of the part while the pick-off spindle supports the part for cutting.

Inspection Process

Parts are collected in the basket for about 20 minutes, then the basket is changed and 5 consecutive parts are taken from the machine as they are made. These parts are inspected. If they pass inspection, the parts (in the basket) are put in a pan with the other good parts that have been made that day. If they do not pass inspection, they are separated from the rest and tagged to be sorted or scrapped.

Learn More about the Davenport at Davenports' web site