At PTP Manufacturing, our goal is to deliver quality parts at a fair price and on time. Many times this means getting creative and using our resources in new ways to accommodate a unique situation. An example of this was producing a tube housing prototype for a new water filter. The company had tried two other plastic machining vendors. Neither company was able to machine the raw tube stock to the required tolerances.
The project was to precision machine a large tube that will contain a water filter. The project required NSF materials and tracing. It also required very tight tolerances. The tight tolerances allow the customer to friction weld the end caps after the filter element is installed. The machine shops they had tried befor coming to us had not been able to meet their needs. Some of the reasons related to the tube’s distortion during standard machining. This distortion caused tolerances to slip out of limits.
As we examined the part’s drawings, knowing that others had not been able to produce the part, we identified what issues were standing in the way. Our experience told us that we would need a way to secure the workpiece during machining and not distort the raw tube. Also, we would need to machine the tube stock in such a away that tool forces would not distort the geometry of the tube. These two issues pointed us to the need for a custom fixture and tooling.
The fixture we designed used custom chuck inserts to spread the holding force needed over a larger surface area and radius. The fixture allowed a secure hold on the part without distorting it.
We also knew that we would need to reduce the point force of the cutting tool. To do this, we would need to produce a custom cutting head. We got out our pencils and spent some time on a Bridgeport milling machine and made a 3 insert cutting head for the project. By cutting at four points of the radius, we were able to spread the tool load and again avoid distorting the geometry of the piece during machining.
The result was a part that met all the tolerances and could be produced at a competitive price.
In another project, we are machining a set of matching parts also for a water control application. This project presented many challenges as well. The parts must mate with a high degree of precision and alignment. They also connect to many external tubes and the products user makes setting adjustments that require labeling.
We designed a fixture plate to accommodate both mating parts. The fixture plate allows us to machine the pieces so that all the water passages align.
The raw material is 2.5” diameter PVC rod purchased in 5’ lengths. Both parts are cut to length and initial machining is done on one of our CNC turning lathes. After turning the parts are moved to one of our CNC mills. The first milling step is to place a face locating hole in each part. Next they go onto a custom fixture. The custom fixture is a plate with orienting pegs for the crossholds. Due to the volume of the order, there was no extra cost to the customer for the custom fixtures.
Designing tailor-made fixtures gives us better quality control. In this case the fixture allows for the holes to be drilled in the exact right locations. For the O ring turning grooves, diameter is critical. We could check this with our gage pins. The pipe threads on the crossholds were measured with our thread gages. These quality control checks gave you confidence in your parts. You are assured that the pieces you receive match your specifications.
Another challenge on this project is the part printing. We have a vendor that we work with that allows us to provide this service to our customers. In this case, we tried laser marking because it is usually the most economical option. However, we were not getting a consistent color with laser marking. The white was changing to gold, which was not approved by the customer. So we arranged to have the part labels added utilizing Pad printing.
The only surface prep necessary was to provide clean parts, which is always our standard. Pad printing is a process that utilizes an etched plate, ink cup, and pad. The ink cup slides over the etched plate to deposit the right amount of ink into the etch. From there the pad is placed on the plate to pick up the image and then transfer to the surface of the part. Having this resource available means that we can be versatile with our printing. Pad printing can be used on a wide array of materials and irregularly shaped surfaces. In this case, we wouldn’t have been able to provide for this customer without it.
This is another example of using custom tooling and fixtures to benefit our customers. We have 2 of each of the fixtures so we use sides of the milling machines pallet. This reduces cycle time and thus part cost.
We have also worked with our customer so that we make 250 pieces at a time. We do this as there is a significant price break on Pad printing at this run size. This also allows us to hold some stock so that if there is a last-minute need we have it on hand and ready to go. Delivery is done with our own trucks so there is no delay.
Having all these tools at our disposal in-house means that we can offer efficiency and a lower cost. We know speed and price matter to our customers. Creating custom fixtures right at our facility is one way we bring you the best service at the lowest cost.