Scratch Building Tires - Diamond Tread Cutting

[wunwinglow]

Jay, you might end up with a marketable product.....

[Guest Paul Budzik]

Correctomundo Jay  ...

 

The indexing head does your spacing and the circular saw only establishes the guideline cuts across the tire,  The slotting (sometimes referred to as a slitting file) really establishes the grooves.  So you still need a good eyeball and steady hand.

 

I have a page on files here:

http://paulbudzik.com/tools-techniques/Files/files.html

 

Paul

[Martinnfb]

Thank You Paul for taking the time and sharing the knowledge , always appreciated .

Cheers

Martin

[wunwinglow]

I'm sure we have purchased slitting saws in different widths in the past. But filing the grooves will give you great control over the depth of the cuts, especially of they feather away a bit rather than have a set deprh.

[JayW]

Paul - that is a very professional article on files.  Once again this type of tool is far more advanced than I had realized (I see that often with different kinds of tools).  GOTTA get a slitting file.  Will be looking for one immediately; my LHS (local hobby shop) has failed me.

 

Oh - patience please for those who would like to see the diamond pattern Thunderbolt tires in 1/18.  They are in the queue behind the P-51 wheels and tires!!  

[alaninaustria]

Damn Paul, thanks for posting that video! Very interesting! I have been wanting to get a vertical mill to compliment my lathe - might have to do that oneday!!

Cheers

Alan

[Red Five]

I'm just doing a car, MG Magnette, to pose next to my DH88 and one issue is that the tires are smooth when they should have tread.

 

My solution is to build up the tread with primer. This may sound time consuming but since I'm re-spoking each wheel I thought I may as well go the whole way. I'll post some pictures in a week or so when I know it's worked.This involves cutting lots of very fine strips of masking tape and lots of patience. 

 

Bit old school I know but I was building Airfix kits in a  day in the 1970s ( and shooting them with an air rifle months later---I don't do that bit anymore). 

 

Andrew

Edited July 13, 2016 by Red Five

[JayW]

Last post was in July of 2016 - a year and a half ago.  Meanwhile.....

 

Just now, I have diamond tread tires for my 1/18 scale P-47 Thunderbolt.  How did I do it?  Well thanks to Bill who gave me a good idea for a saw cutting jig in this topic thread, I did a version of that idea.  I will start from the beginning.

 

First one must be able to manufacture or acquire a smooth tire.  Mine is a lathe turned acrylic one.  Here it is mostly complete on the lathe:

 

 

 

And finished:

 

 

At this point one must decide on the tread pattern - how many rows, etc.  For me that meant researching as many period photos as I could find and hoping I guessed about right.  In the end I decided the tire needed 28 rows, with alternating rows of three complete diamonds, and two complete diamonds with two half diamonds.  Then, a layout is required to determine the required angle of a straight saw cut.  Draw a rectangle of arbitrary length (but long enough to draw several rows of diamonds) and a width that accurately represents the unwrapped width of the desired tread pattern.  Here again I studied old photos to decide how far down the sidewall I wanted the tread to extend.  Use a large scale so as to minimize error.  You know that each diamond will be the diameter of the tire times pi divided by the number of rows (in my case 28).  The width of the diamond is the unwrapped width of the tread pattern divided by how many complete diamonds you want (in my case three).  The cut angle is then easily generated.  In my case it was 41.5 degrees from the centerline of the tire (83 deg for the completed diamond shape, nearly square but not quite).

 

Now one must able to accurately maintain the cut angle for each cut, and accurately maintain the spacing of each cut.  If you want to use a saw (that is what I decided), then you need a nice stout jig.  Here it is:

 

 

 

You see the jig itself with upright posts to guide the saw blade and control its cut angle, a wide slot in which to insert the tire, cradle slots in which to support the axle, and a fixed pin protruding from the near side that engages a geared wheel.  You also see the tire with special wheels, one of which is slotted to accept a cross pin on the axle.  And you see the axle itself with its cross pin and a geared wheel (28 teeth) bonded to it.  The teeth are meant to engage in the fixed pin on the jig, and meant to control the spacing of each cut.  Got it?

 

Here is the setup with the first cut accomplished:

 

 

And more cuts:

 

 

Now truth be told, this jig had some problems.  There is slop between the axle cross pin and its slot on the wheel, which allows some free rotation.  Also the spacing between the upright posts is a bit generous which allows the saw blade to wander a bit.  Add those up, and the diamond pattern becomes inconsistent, with unequal distance between rows such that some diamonds are larger than others, and/or mis-shapen.  Which is exactly what we do not want.

 

So I made modifications.  One, I added thicker shims to the sides of the saw blades such that the saw barely fit between the uprights thus eliminating any wiggle with the saw blade.  Two, I created equidistant drill starts on the OD of the tire, giving me a target in which to center the saw cut (I could rotate the tire within limits due to the slop between the cross pin and its slot).  And third, most importantly, I applied clamps to the jig once the tire was exactly positioned for the cut.

 

Some pics of the modifications:

 

 

 

This gave me a good result:

 

 

Were I to do it over, I would redesign the jig such that its posts were taller (allows for the cut to better wrap around the tire),and each pair of posts would be oriented perpendicular to the direction of cut, not the direction of the tire center plane.  That would provide a stiffer support for the saw blade.  I'd also want a slightly taller saw.

 

I want to thank (belatedly) all those modelers who contributed to this post.  You gave me great ideas.  I hope you like my solution and my result.  And I hope it may help some of you in similar endeavors. 

Edited February 27, 2018 by JayW

[kman458]

I have done something like this before.It will sound confusing till you a wheel and try it because I know how it works but have issues describing it.

 

Draw a line centered on the center of the tread. Mark how many treads you want and and divide the center line with that amount. Draw a line from one of those marks perpendicular to the tire center line and ending at the edge of where the tread will to be. Divide the edge of the tread to the same amount of marks. Now all you need to do is draw a line from one of the side marks threw one in the tread center and over to the other side. With this you can make different patterns depending on what marks you use.

[JayW]

Pretty slick there Kman.  Only thing is - you have three points, now how do you make a good cut around an elliptical (or nearly) surface.  Do you not still need some sort of guide? 

[kman458]

Pretty slick there Kman.  Only thing is - you have three points, now how do you make a good cut around an elliptical (or nearly) surface.  Do you not still need some sort of guide?

 

I have a small pull saw that would be the ticket. Since the tires are pretty flat the line is pretty straight.

[kman458]

Pretty slick there Kman. Only thing is - you have three points, now how do you make a good cut around an elliptical (or nearly) surface. Do you not still need some sort of guide?

 

I have a small pull saw that would be the ticket. Since the tires are pretty flat the line is pretty straight.

I do have to say your jig looks pretty good

Edited March 3, 2018 by kman458

[sandokan]

Wow!! What interesting trick!!!!!! Thanks guys!