Author: Bob Hunt
Edition: Model Aviation - 2011/03
Page Numbers: 131,132
,

Control Line Aerobatics

Bob Hunt <[email protected]>

Sanding tools that should be in your shop

It's time to get back to our discussion of properly setting up and equipping a shop to build a CL Aerobatics (Stunt)—or any other type of—model. Before beginning I'd like to extend a "Thank you" to all who have written, called, and/or e‑mailed me about the "shop setup" series.

In all the years that I've been writing columns, no other subject that I've covered has been as well received as this one. It seems that many want and enjoy tips on shop setup and tools.

I left off in the September 2010 column with a discussion of sanding tools. I promised then that I would tell you what I feel are the best and most useful kinds available. No more suspense; it's Perma-Grit!

What is Perma-Grit? It's a line of sanding, filing, and grinding implements that feature bits of tungsten welded to metal plates, sticks, and grinding bits. The tools are indispensable for quality, efficient, and effortless model building.

I purchase all of my Perma-Grit products from Bob Violett Models (BVM). The web site shows all of the Perma-Grit tools that BVM carries.

There are so many different and unusual Perma-Grit tools that a complete discussion of them here would be impossible. Instead I'll give you the skinny on my favorite instruments in the company's line and tell you why they are just that.

Without a doubt, the Perma-Grit tool I use most in my shop is the 22-inch-long Sanding Block (item SB-560). It features two Perma-Grit sanding strips: one fine-grit side and one coarse-grit side.

The sanding strips are adhered to a precision aluminum extrusion that measures 2 inches wide by 1-9/16 inches high by 22 inches long. The same height-and-width extrusion is available in two shorter lengths, and one of those features wedge-shaped ends to allow easy access into tight areas.

I use the 22-inch Sanding Block for many modeling jobs. It's great for truing the LEs and TEs on freshly covered foam-core wings and works well when shaping foam fuselage top and bottom bucks that will be used for making molded shells. However, my favorite use for this tool is truing the edges of balsa sheeting pieces that have been edge-trimmed with a knife.

To achieve a perfect square edge that will fit together with no gaps and will butt-glue accurately, set the Sanding Block on its side (the extrusion that the bar is based on is so accurate that it presents a square side no matter which edge it is laid on). Position it against the edge of a piece of 3/4-inch-thick chipboard or plywood.

Lay a trimmed balsa sheet on the chipboard, against the fine-side edge of the Sanding Block. Then use a Great Planes aluminum sanding bar fitted with 80-grit sandpaper to hold the balsa sheet down against the chipboard and the edge against the Sanding Block. Push the balsa sheet fore and aft against the bar until the edge is trued.

I've included a photo of this process that (I hope) will explain it better. With the edges trued in this manner, you can achieve a fit that is airtight, requires little glue, and won't show later when you apply the finish to the model.

Another pesky job is smoothly blending a soft balsa surface into a hard surface, such as plywood, without having a lump or depression where the dissimilar materials meet. On a CL Stunt model this would include blending the fuselage sides into the top block and the cowl block where they meet the spinner. There are usually plywood doublers beneath the balsa fuselage sides, and they need to be blended in a compound curve to flow smoothly into the spinner.

Several Perma-Grit tools make this job easy, such as the Flat Full Length Hand Tools (items F-100, F-101, and F-102). Each measures 9 x 1-1/2 inches and comes in three grits. These instruments provide precise sanding and are extremely easy to control, accomplishing the required blending of soft materials to hard.

I've included a photo that shows the nose of a typical CL Stunt model that was sanded to shape using a Flat Full Length Hand Tool. This job used to be a nightmare for me; now, with the help of Perma-Grit, it's easy!

I have a complete set of Perma-Grit Hand Tools that came in a pouch. I don't see that grouping on the BVM web site, but all of the implements in the set that I have are available separately, so you can choose which ones will work best for your aeromodeling applications. I'll bet that when you get one, you'll soon order all of them!

These tools are available in a variety of shapes, including several constant-diameter rounds, angles, concaves, and half rounds. I'm including a photo of the pieces that came in my set.

Another great Perma-Grit offering is the Flexible Strip (items FXT-103 and FXT-104). The two types are essentially the same sandpaper pieces that are adhered to the extruded sanding bars, but they are sold separately. These strips can be used in the manner of the Flat Full Length Hand Tool for deft shaping, and they can be cut with tin snips to any size or length you desire.

I have cut a 3/4-inch-wide piece off of one of the strips and use it as a tool with which to open hinge slots to a perfect size, to allow the hinge to slide in without spreading the wood on either side. It has made hinging painless!

An indispensable Perma-Grit item is the Needle File set (item NF-1). These tools come with comfortable handles and are great for working in small areas and with materials with which regular needle files have trouble.

There is also a huge selection of Perma-Grit Rotary Files (grinding bits). My favorite is the 10mm diameter ball (item RF-8c), which is wonderful for hogging out the majority of balsa when hollowing a cowl block or carved-balsa wingtip blocks. Other rotary tools include a selection of cutting disks.

A Perma-Grit video is available that explains each tool and suggests many ways to effectively use it on balsa, plywood, and composites. It also shows how to clean and care for your Perma-Grit tools. Do yourself a favor and get a copy of this DVD before you start using your purchases.

This line of tools truly needs to be in every modeler's shop. These implements are not inexpensive, but they are priceless!

Till next time, build and fly Stunt! MA

Sources:

Transcribed from original scans by AI. Minor OCR errors may remain.