Frequently Asked Questions (FAQs)
1. What tolerances can Seward Screw hold?
Tolerances vary depending on the type and grade of the raw material we are machining, the material that we make the tools out of, and the machine we use to make a particular part. Tighter tolerances can be achieved with secondary operations such as grinding, honing, and lapping. A broad-based answer to this question is difficult to provide. It is
best to answer this question on a part-by-part basis in an engineering review.
2. When are products best made on multiple spindle automatic screw machines?
Screw machines are best used for parts with batch volumes of 2,000 pieces or more. Part geometries that are best for screw machines are parts with features that are put onto the part in the same plane, or perpendicular to the plane on the outside of the part. In screw machines the bar is turning and the tools are stationary, so certain features are difficult or impossible to achieve with this process.
3. What would qualify as a "CNC turned product" versus a "screw machined product?"
CNC describes a lot of different machine types, the common denominator being that there is a computer that controls the machine’s axes. CNC lathes are typically faster to changeover than screw machines, but depending on the features of a part, may have longer cycle times to complete the machining than a multi spindle screw machine. There are CNC multiple spindle screw machines, and we have one at Seward Screw. It combines the six spindles with three axes of machine movement so it is essentially an 18 axis lathe. The bar is stationary in a CNC lathe, and the tools do the turning. With shorter changeover times, CNC lathes are often used to make lower volume parts, such as 100, 200, or 500 piece batches. They can be used for higher volumes, though.
4. What would qualify as a "rotary transfer machined product" versus a "screw machined product?"
A rotary transfer machine makes parts with multiple features, perhaps on both ends of the part, and in planes perpendicular or not. The bar is cut off and the starting piece of material is held in a collet and as the machine indexes, the part travels from tool position to tool position in the collet. Each of the stations in a rotary transfer machine has an independently controlled motor and feed system, making it possible to do many features. The rotary transfer machines at Seward Screw Products have 10 or 12 stations. Since these machines are very setup intensive, high part volumes such as 25,000 pieces are best for these machines.
5. What are your minimum run quantities?
Since we have so many different types of machines, the minimum runs vary by the type of machine we have. We are willing to vary the run quantities to what makes sense with the individual customer’s needs, and the quoted prices reflect that. We have indicated some volume references in the questions 3, 4, and 5.
6. What kinds of materials is Seward Screw capable of machining?
Low and medium carbon steels, alloy steels, stainless steels, copper and copper alloys such as brass and bronze, aluminum. These can be in bar or tube form.
7. What is your average lead-time?
New parts take longer due to tool layout, design, purchase and manufacture, gage selection and purchase. We typically figure one week per operation that we perform on a part. Time to get ready for that start can be a week or two on an existing part, and it can be four to six weeks or more on first-time parts. The current parts we make average about three to four operations, with a range of one to 16.
8. Your price looks good for higher quantities, but I don't want to stock that many parts . . . what is Seward Screw willing to do?
No one seems to want to carry inventory any more. We can negotiate some sort of agreement on larger batch sizes, but would expect the parts to be taken in multiple releases over a negotiated reasonable period of time. Customers who can’t commit to larger batches do not get to take advantage of those economies in the quoted prices.
9. Does Seward Screw offer new part design assistance or suggest changes that would save money on existing parts?
Yes, we do. In fact, we have had a lot of success with this service and many of our customers value this.
10. Are screw machine parts "screws"?
Screws can be made on screw machines, but common screws and bolts are typically made on much more efficient machines like headers and threaders. Our company is named for the type of machines we had when founded. But we make very few parts that even look like screws.