Talking About Tolerances

A major consideration on most parts we work on is tolerances, IE. how far can our fabrication work deviate from the dimensions on the drawing. Several issues keep coming up with tolerances and it’s something you need to actively think about for your application. The first major issue we get is unreasonable tolerance requests. This can be anything from a customer accepting zero deviation from the drawing, which is impossible, to passively leaving metal tolerance requirements on a drawing that simply cannot be held with a plastic.

There’s another issue that does not get considered enough which is when customers tell us to hold “best possible tolerances” because they don’t know what they actually need. This tolerance, often (+/-) 0.005″, results in a higher cost for the part as it’s more difficult to make with less margin for error. The fact that there are actual costs to “best tolerances” is something the customer should know.

The other issue with tolerances is that the difficulty of holding them depends on the material. For example, it is much easier to hold a (+/-) 0.01″ tolerance on acetal than it is on a rubber product. Absolutely the rule “one size fits all” does not apply. You also really need to think about the application: a bushing which is press fit into a housing and has a shaft going through it with a running clearance needs more precise tolerances than a polyurethane bumper.

For more information on tolerances or a quote on your requirements, please contact us today.

UHMW vs. PTFE

There are few questions we dread more than the customer asking about a PTFE truck liner. While the error is understandable – in natural form both UHMW polyethylene and PTFE are white colored plastic, if PTFE were ever used as a truck liner the cost would be many 10s of thousands of dollars and the liner would be worn to bits in short order! Yet, monthly we receive inquiries from customers who simply don’t know any better asking for that. We believe it’s important to discuss the distinction, and some similarities, between the two plastics.

Similarities:

Both plastics in their natural form are white and both are widely stocked by most plastics distributors. Both plastics are known for having a very low coefficient of friction and net zero water absorption. They’re both available in 48″ wide plates and in common thicknesses from 1/8″-2″ (and beyond). Both plastics are FDA/CFIA compliant in their natural form. Both plastics can be modified with a variety of fillers or additives. However, that’s where the similarities end.

Differences:

There are so many differences between the products that a list is the best way to explain:

  • PTFE is substantially much more expensive than UHMW
  • PTFE can only handle about 1/5th the load of UHMW
  • PTFE is more slippery than UHMW (despite both having a low coefficient of friction)
  • UHMW has far better wear properties than PTFE
  • UHMW is typically stocked in 48″ x 120″ sheets where PTFE comes in 48″ x 48″ plates
  • PTFE withstands over 4x the temperature UHMW can in continuous operation

So if UHMW is less expensive, handles more wear, and more load…Where do you use PTFE? The answer is pretty simple: 1.) when it’s spec’d in or 2.) when one of its differing properties from UHMW makes it the better choice. For example, if you’re machining some bushings for use in a 400 degree Fahrenheit environment you would go with a PTFE product vs. a UHMW product which would simply melt. As well, if the application demands bearing pads with dynamic sliding (think telescope mounts) then PTFE is the better choice due to its phenomenal low coeffecient of friction. If in doubt, simply contact Redwood Plastics and Rubber and we’ll lend a hand!

Shark Fin Board Turning System: Ideal Applications

The venerable Shark Fin Board Turning system has provided saw and planar mills with decades of excellent performance across the world. The system is simple, using the mill’s existing machinery and gravity to turn boards. This frees graders from this responsibility which leads to reduced injury claims and increased productivity. However, the Shark Fin is not ideal in all circumstances. Modern mills, particularly softwood mills, run too quickly for Shark Fin to function. Shark Fin is ideal in any application that runs 75 lugs-per-minute (LPM) or less, this is typically hardwood mills these days.

The Shark Fin is also not designed for very small tables. The minimum size for a one grader table should be about eight feet in length and the table needs to allow for Shark Fin lugs that are approximately 7″ tall to travel over and around. The system also requires that it be used on 81X sawmill chain as the lugs, pins, channel and other components are designed for it. The system succeeds in mills that want a simple, low-cost grading solution where their employees are handy and able to work with a kit.

So what does a Shark Fin kit consist of?

-Shark Fin turners

-Shark Fin lugs

-Shark Fin pins welded onto 81X chain

-81X channel

-Polyurethane drive and idler sprockets

-Bearings, collars, and steel shafts

-A spare parts kit

For questions about the Redco Shark Fin system or for a quote on your needs please contact us.

Video of Shark Fin in action!

3 Tips For An Easy Rubber Purchase

Purchasing rubber would seem to be a simple thing: everyone knows what “rubber” is and most people think of it as one hegemonic product where even if different rubber types exist, they’re all more or less similar. That is actually untrue and the rubber family is indeed much wider, more extensive, and perhaps complicated than most people might think. The good news is help is available! We are rubber experts here and can carefully guide you through the process of selecting the correct Redco rubber for your application. However, if you feel you have a pretty good handle on rubber and don’t have a need to go through the selection process with us, these three tips will help ensure anyone is satisfied with a hassle-free rubber purchasing experience.

#1 – Know Thy Rubber

Even if you have a pretty good handle on rubber products you do need to make sure you “know enough”. Here is an example, you’ve used SBR rubber before and you know what size and thickness you need it in, perhaps 1/8″. So you email an RFQ “I need one piece of SBR 4′ x 8′ x 1/8″ ” Is that enough information? Actually it isn’t. We offer SBR in both 60A and 80A durometer (hardness) and we need to know which you need. In addition, we offer almost all of our products in a premium grade, which can be provided with certifications, and consumer grade, which cannot be certified beyond a simple compliancy form. Which leads to…

#2 – Know Thy Certifications

One stressful part of the rubber sales process for both the salesperson and the customer, is when certifications are requested after a sale and after the rubber has been shipped. While one may assume that all rubber we sell is certifiable and to any industry spec, this is actually inaccurate. It can lead to annoying situations and even cancelled orders. Our lower-priced consumer grade product offers price savings but cannot be certified for, example, food processing or aerospace requirements. We do offer such grades of rubber! However, those are our premium grade materials. Therefore please always inform us of any certification that is required before purchasing. In addition, we have run into certifications we cannot supply – even with our premium grade materials, which is why it’s best to bring any certs up during the quotation stage of the process.

#3 – Ask and Trust

If you’re unclear at all about what rubber you require, please do not hesitate in asking for help. At times, customers may feel ashamed admitting they need help in picking a product. However, as long as you can get us the information we need on the operational environment of the application we are happy to help make a recommendation. That said, there is a measure of trust involved. Customers tend to be familiar with “neoprene” rubber, for example, but when we’re telling a customer he/she needs Viton P70 rubber to function in the application then trust comes into play.

You can view our rubber line card by clicking here.

For more assistance or a quote on your rubber needs please contact us today.

Product Spotlight: Pile Driving Cushions

Redco IRG (impact-resistant grade) nylon pile driving cushions are one of our core products for the construction industry. These pads are hand-made to fit into each customer’s pile stacks and absorb the impact of the hammer, dissipating the energy as heat. Unlike regular grades of nylon, which are brittle to impact, IRG nylon is filled with plasticizers and heat-dissipation additives which allow it to absorb the huge impact involved. The cushions can be manufactured for any foreseeable size, typical tolerances are (+/-) 1/8″ or 1/16″ with the standard color blue. Typical manufacturing time is 5-6 weeks to ship an order.

For more information on our Redco Pile Driving Cushions click here to view our literature or contact us for a quote.

Pile_Cushions_HEB

Three Preparation Steps For Part Design

So, you have a part you want made out of plastic (or rubber). You have a drawing, maybe a CAD file. You know what the part needs to do.

What now?

This is the stage where you need to make the leap from idea to practical. To get the part finalized, material specified, and actually get the part into production. What information do you need to have to finalize everything?

1.) Know Your Operational Environment

This is absolutely critical and something we often need to work through with customers before we make a recommendation. You need to know the complete operational environment for your part. This includes:

  • Min/Max operating temperature
  • Chemical exposure (and how much exposure to each chemical – it matters!)
  • UV-exposure
  • Pressure applied on the part (in PSI)

Depending on the part there may be other critical factors but you should know at least those four.

2.) Know Your Required Tolerances

This is perhaps the most important thing that keeps getting overlooked in part design. Often we’re handed a drawing with metal tolerances (+/- 0.001″) and told to make it (hint: not possible to hold those tolerances). Or, in many cases, customers simply tell us to hold “best” tolerances. Did you know there’s a premium to that? When we work out a quote internally, required tolerances are part of that because of the time and risk involved in hitting our tightest (+/- 0.005″) tolerance. Often a (+/-) 0.03″ is suitable for many applications and since it will save you money, it’s worth it to know the demands of your application.

3.) Know Your Quantities – Buy In Bulk

Quantity usually means price break when it comes to parts. Customers will often send us a drawing and ask that we quote a couple pieces, ostensibly as samples. The issue is that the cost for prototypes will be inflated compared to the prototypes…And sometimes customers just think the price would remain constant. So know an accurate number of how many parts you will need once in production and get both prototypes and production runs quoted at once for a clear picture of your costs.

For more information on how to buy your parts in the most economical way possible, please contact us today.

 

 

 

5 Things You Need To Know For Your Twin-Wall Polycarbonate Install

Twin-wall polycarbonate is a long-lasting and cost effective product that can provide years of enjoyment in a greenhouse or roof awning application. The product is durable, UV-resistant, and relatively inexpensive. However, there are some very important things you need to know to maximize the success of the product and avoid premature degradation.

Only use mild soap and water to clean

While polycarbonate is very strong in regards to impact, it is prone to scratching. Using harsh chemicals or dirty water could mar the surface. Make sure to change the soapy water often while washing the twin wall to avoid grit damaging the surface.

Always install with the film facing outwards

Only one side of twin wall polycarbonate comes with a UV-protective film, which is often clear or light blue. The other side is often masked to protect against scratches and UV but meant to be peeled once installed.

Use a rubber coated washer when you fasten

When you screw in the twin wall to the frame be sure the screws have rubber coated washers. These reduce the pressure on the plastic because remember it is made up of thin walls.

Store in a dark area

If you’re not installing the twin wall right away, store it in a dark area like a garage. The UV mask does not last forever and you will be using up needlessly the sun exposure meant for the product when installed. In addition, the masking can become difficult to remove when exposed to light and heat.

Don’t worry about tapping a large screw hole

Twin wall polycarbonate expands and contracts due to heat to the ratio of 1/8″ per 100 degrees Fahrenheit of change. Having a larger screw hole will provide some important ‘give’ during temperature fluctuations.

For assistance and a quotation on your polycarbonate twin-wall needs, please contact us today.