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ABSSAC is an established supplier of miniature precision lead screws, encompassing power and high helix thread forms. With well over 3 decades of application experience they have been assisting engineers specify the correct linear product into an ever expanding range of applications. With a range of matching nuts to suit a myriad of performances as well as the facility of a fast turnaround machine shop allowing the lead screw and nut program to be delivered, ready to fit. Using the machine shop also reduces customer scrap rates. Find the right product for the right price, including support bearings, racks and splines and other related ancillary products.
There are 3 basic ways to make the lead screw thread, those being, rolling, whirling and grinding. Each method has its advantages and disadvantages so let’s look at each method individually. Here is some basic product information, that may be useful.
The thread form is squeezed into the bar of material using dies under high force. This method makes a thread with a really good sliding surface finish and the process is quick. As the rolling process compresses the material it also superficially hardens the working area of the thread. The majority of our threads are rolled. The disadvantage to a rolled thread is at that very high precision isn’t possible. Most rolled threads are 2G, with care we can roll most sizes to 3G but 4G is too much for rolling.
The thread is machined rather than formed as it is in rolling. This means the thread is high accuracy but doesn’t have great surface finish nor is it hardened. This thread (with natural finish i.e. uncoated) is not suitable for use of plastic nuts due to surface finish.
Very precise thread can be created in hardened materials but you have limited choice of sizes and thread forms. The process is also labour intensive which makes them a higher price and longer delivery time than the other methods. A ground thread is normally used where accuracy is of upmost importance.
As standard, most rolled lead screws are made from 300 series Stainless Steel. These materials form well, give a great surface finish and have good corrosion resistance. For a ground screw, something like 440C or 17-4pH works well as it is a grade of stainless which can achieve sufficient hardness. But these types of Stainless doesn’t have the corrosion resistance of 300 series. Customers like the thought of 440C or 17-4pH because of its hardness but unless it’s a ground thread, it is difficult to machine and doesn’t leave a great surface finish.
Several types of material can be used for the lead screw nut. The material you choose for the nut depends on the application. Broadly speaking, you have 3 nut materials; Steel, Copper Alloy or Polymer (Plastic)
Steel - Used for high loads at low speed.
Copper Alloy (Bronze) - Bronze nuts are very popular for lead screws. There is a vast choice of bronzes to choose from, such as Leaded (Pb) Bronze, SAE660 or Sigma 7 Bronze are also popular choices. (The Pb in the material reduces the sliding friction between nut and screw). Materials with higher strength include Tin Bronzes (PB102) and Alu Bronzes (CA104) but these have more friction than the Pb Bronze, less tolerant of lack of alignment, lubrication and shock loads.
Polymers - The number of plastics suitable to make lead screw nuts is almost endless however, there are several that have become the industry norm. Plastics are useful because in the main they are low friction and require little if any lubrication.
Lead Screw Coating
Various coatings can be applied to the screw to reduce friction of the mating part. PTFE based coatings can have very low coefficient of friction but can be quite soft and can be rubbed off by abrasion of even a plastic nut with bronze nuts wearing through it quickly.
Machining lead screws
Let’s work together to reduce your scrap rates and supply leadscrew solutions that fit directly into your application, every time. With a machining capability that is enjoyed by numerous ABSSAC customers the company provides an excellent journal concentricity product, regardless of diameter. ABSSAC can work directly from dimensional drawings or if they do not exist, they accept the physical sample for them to reverse engineer. Although all types of end machine detail can be employed ABSSAC offers a very competitive basic end journal machining that fits their range of support bearings
Mr Phil Jones of Abssac says, “We have had great success in reverse engineering original designs of lead and ball screws where no formal drawing exists. Customers have shipped the parts for us to dimensionally check and copy into a new physical part. It is particularly great to get involved with these types of projects where we are part of a restoration. Abssac has a huge range of linear products, so nine times out of ten we can help with these more unusual requirements”
ABSSAC also supplies a full range of linear guides and rails which can provide the load support to a linear mechanism. Offering excellent rigidity and parallelism during operation the guides can be used in both vertical and horizontal planes. The whole program allows ABSSAC to supply a complete linear system, which they will assemble for you as well if required. Should you require further technical information, please do not hesitate to contact ABSSAC sales engineers who will be more than happy to help you with your selection.
ABSSAC is also constantly investigating ways in which linear solutions are made more affordable. One method has been to employ plastic moulding injection techniques for the lead screw nut bodies. Then instead of machining the lead screw form , they have utilised cold rolling precision methods. Both methods significantly reduce unit cost and as shown in the image has no detriment to form and function. The lead screw shown below is a cold rolled formed 7 start, Stainless Steel screw with a lead accuracy of .25mm per 300mm of travel. (14TPI .250inch diameter .500inch lead). If you currently use lead screw and nut combinations in your application why not set ABSSAC the challenge to prove their affordable solutions.