DLG Foam Cutting

by Jay Decker

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Basic Equipment

JSD - Foam, current source 01.jpg (60887 bytes)

Current Source. The current source for my system is autotransformer, also known as a "Variac", and a fixed transformer. The fixed transformer plugs into the Variac. This is a very safe and finely adjustable current source.

JSD - Foam, cutting bow 01.jpg (36305 bytes)

Foam Cutting Bows. My bows are "strung" with 0.020 inconel cutting wire. The frame is 1 x 2 poplar and 0.040 stainless steel  is strung around the back of the bow. Small turnbuckles are used to increase the tension of the wire. The bow pictured is a 20 inch bow and used most often.

JSD - Foam, cutting bow hanging from ceiling 01.jpg (71325 bytes)

36 inch Foam Cutting Bow. Many guys get into foam cutting with thought that they can accurately cut 48 inch long cores -- wire drag makes that very difficult. If you limit your maximum cut to somewhere around 30 inches you'll greatly improve your accuracy, particularly with Spyder and other denser foams.

Blocking Foam

JSD - Foam, Blocking  01.jpg (72722 bytes)

I like to accurately block foam. This is a photo of a cut in progress. The cutting wire is guided by the jigs clamped to the table. If you looks closely you'll see that the cutting wire is pulled against the guide with a small tension spring. The weight of the bow provides the downward force to cut the foam.

JSD - Foam, Blocking 02.jpg (62651 bytes)

If you look closely at the bottom of the guide, you'll notice a small notch filed into the guide which catches the bow, incase I don't catch the bow when the cut has completed. Notice also that the tension spring is mounted on a pivot.

Cutting Cores

JSD - Foam, making bottom cut 01.jpg (61499 bytes)

This is a photo of a bottom cut in progress. I use two piece templates and make the bottom cut first. The bow is suspended from a string attached to the ceiling. The cut is from leading to trailing edge.

JSD - Foam, making top cut 02.jpg (54704 bytes)

Here is a top cut in progress. My particular cutting system is an old system that uses belts with teeth that engage pulleys of different sizes to achieve varying core tapers.

JSD - Foam, making top cut 01.jpg (49615 bytes)

This photo shows the large T-pins that are used to attach the templates to the foam block.

The bottom cut for Spyder foam SuperGee cores in progress. Notice the weights on each end of the cutting bow; the weights are attached with Velcro. The weights help the cutting wire "drop" down into the leading edge of the bottom core cut.

The weights are not used for the top cut -- they impede the wire climbing the leading edge.

If you are looking for a good foam cutter that you can build yourself check out:

Automatic Foam Cutter

Pivot Cutting

 JSD - Foam, 2 Template Pivot Cut 03.jpg (60142 bytes)

For cores with sever taper ratios, e.g., DLG tips, I use a pivot cut. I use templates at each end of the block for greatest airfoil accuracy.

 JSD - Foam, 2 Template Pivot Cut 01.jpg (58428 bytes)

Since the pivot end of the bow does not move only one source of tension is needed to move the bow through the foam.

JSD - Foam, 2 Template Pivot Cut 06.jpg (66445 bytes)

This photo shows two parallel guides being used to slice block in half horizontally. Each half will be used for a DLG tip panel.

JSD - Foam, 2 Template Pivot Cut 08.jpg (56872 bytes)

This photo shows the foam block mounted on a piece of 1/4 inch balsa while the bottom cut is in progress. The balsa block raises the bow high enough so that the ends of the bow do not drag on the table.

JSD - Foam, 2 Template Pivot Cut 09.jpg (49740 bytes)

This photo shows a notch pivot which is attached to the table with double side stick tape.

Completed Cores

JSD - Foam, completed inner core 01.jpg (41926 bytes)

Freshly completed UpLink inner wing panel.

JSD - Foam, completed 2 in tip pannel 01.jpg (49909 bytes)

2 inch Uplink wing tip panel standing on end.

JSD - Foam, completed UpLink wing cores 02.jpg (58930 bytes)

Completed UpLink wing panels and templates.

 JSD - Foam, completed UpLink wing cores 04.jpg (91270 bytes)

Completed Uplink wing panels and templates.

   
Photos by Jay Decker, email address:

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