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tjones87

Scratch building a frame/chassis

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I am going to try and scratch build a hot rod frame and was just wondering if anyone had any advice? Whats the best size tubing to use? Also is it easier to use square/rectangle tubing than round tubing? any tips or recommendations are greatly appreciated...thanks

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Hi,

I do this a lot. Probably almost half of my projects in the past year have involved scratch built hot rod frames, almost always out of necessity. Mainly it’s been because the body I have been using doesn’t accommodate a kit frame, or the subject matter simply doesn’t have an existing frame in a kit.

It is not entirely out of necessity. I get a lot of pleasure out of building frames – it brings me closer to building the “whole car” and makes modeling less like kit assembly.

I build frames out of styrene strip or styrene rod, depending on the subject matter and what I’m trying to accomplish. Most of the time some part of the frame will show when doing a hot rod, particularly an open wheeled one, so this is a critical issue. A third alternative is to use parts of an existing kit frame, extensively modified.

The most important thing is to keep the frame strong and square as you build it up. Many builders who do this kind of work do it on a surface that’s marked out in a grid of squares, like graph paper, as a way to guide them in keeping their angles in line. It’s not something I have done personally up to now, but it’s an excellent approach and one I plan on adopting with my next frame build.

As regards size of strip or rod stock you use, the most common mistake I have seen, and made myself, is to use stock that is too big. For example, 1/8” styrene tubing or rod scales out in 1/25th scale to 25 x .125 = 3.125”. This is a big diameter member in a frame and looks big to the eye in scale. If anything most builds benefit from the stock being underscale, looking finer and more detailed. My favorite round rod or tubing diameter for builds is the smallest styrene tubing diameter, 3/32” which in 1/25th scale comes out to 2.34375”, or 2.5” to the eye. Styrene rod is available in much smaller diameters. In general using hollow tubing for frame building, as opposed to solid rod, has no real advantage.

The same point can be made for styrene strip, which you can think of as imitating rectangular tubing. So, for example, if you want to make a 2” x 4” frame member, then in 1/25th the strip you would use would be .08” x .16”. Again, if the strip you use is slightly undersized then it may be inaccurate but it will “eyeball” well in the overall build.

I build almost exclusively in styrene, rather than, for example, in brass or aluminum. In modeling, brass requires soldering, a skill I don’t have. Similarly, joining aluminum is generally done using epoxy cement. There are several advantages to using styrene over other materials. The biggest advantage is that it “welds” easily using solvent liquid cements whose main ingredient is methyl ethyl ketone (MEK). Examples of this are Tamiya Extra Thin, Testors Liquid Cement, Ambroid Pro Weld, Plastruct Plastic Weld and Tenax 7. Personally I use the raw ingredient itself, MEK, which I buy at the hardware store in pints. Cheap, plentiful, and I don’t care if it evaporates as I work because a pint will last me a very long time.

The advantage is that you can assemble the frame elements with a weak joint, making sure things are properly lined up, and then go back and brush each joint with more cement which will wick into the cracks in the joint and dissolve the styrene surface, welding the joint together and helping to close up any remaining gaps. Like a real 1:1 metallic weld, the result is exceptionally strong and rigid.

To make sure my joints are in proper alignment I use various methods. The most common and important one is to pin all my joints. You can use either thin styrene rod or metal wire such .020” piano wire or brass rod. I use both. The metal wire is stronger, but the styrene rod will dissolve into the neighboring styrene if you applying cement to it. Pinning your joints locks in the alignment and strengthens the connection. The downside is that it requires a ton of time consuming and tedious pre-drilling as you work. But the first time your frame elements shift on you and a rectangle becomes a rhomboid, you’ll start pinning with a vengeance, trust me!

For round tubing or rod it’s critical to “fishmouth” the ends so that you get full contact between the two pieces.

Another technique is to use simple jigs by laying out the angles on paper and then transferring them to a piece of wood and making rows of small nails or brads to hold the frame elements in alignment.

And yet another technique I use a lot is to actually clamp the strip or rod to the bodywork to shape the frame element to the car and then make the crossmembers to fit. This ensures a tight, accurate fit and is very effective when making highboys, for example.

This is a very big subject and could easily warrant a series of articles or short book. I’ve tried to limit it to some key points and to avoid pictures in my response so as not to hog the thread. I’m far from the most skilled or experienced frame builder on this board so I’m confident others will chime in with greater detail and advice than I can provide, but perhaps this will help to get you thinking in this direction.

I encourage you to try your hand it. Building your own frames is a powerful modeling tool than can open up a wealth of new horizons, and is extremely satisfying in its own right.

Edited by Bernard Kron

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Thanks Bernard, that helped out alot...I believe I am going to use the grid(graph paper) for a building surface...to keep it as square as possible. Won't know exactly what I will need until I find a body to use...I am sure it might take a time or two to get it perfect, but if it doesn't turn out good I can always scrap the styrene and re-use it again on something else.... I have been looking at styrene strips and rod and think I am going to use .060" x 1/8" rectangle strip for the frame rails and either .10" round rod or .10" square rod for the cross-members and bracing...which would be/look better? I', not too worried about it being perfectly like a 1:1 frame since the concept of the build is pretty impractical in itself lol....thanks again for the info and I will hopefully be starting soon...

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Are you building a drag car or a traditional hot rod.? Is it open wheeled or full fendered? High boy or channeled? These questions have to do with how much frame will show. Sounds like your not going the realism route. My feeling about square vs. round stock has more to do with the last issue - realism. Round stock is stronger in the 1:1 world for the same weight, but somewhat more difficult to handle what with fishmouthing and all. Also, square stock in the 1:1 world can be cheaper since it can be formed from flat stock and welded with a seam, whereas seamed round tubing is much weaker than seamless round - again in the 1:1 world. So, from a modeling point of view, round frame members mixed with square elements has a more "fabricated" or "racing" look, whereas going the all square stock route looks either production-like or, on the other extreme, cheaper and less tech. I've done them both. If the frame will be hidden under a body then these issues are all somewhat moot...

Here are some examples:

Stryene strip for the side rails with the front curvature traced from a set of '32 Ford rails. Mixed square and round cross members with an AMT '29 Ford front cross member and and Revell Deuce center crossmember.

th_DSCF2255-web.jpg th_DSCF2259-web.jpg th_DSCF2714-web.jpg th_DSCF2729-web.jpg

(Click on picture for larger image)

Stryene strip for the side rails with the front curvature traced from a set of '32 Ford rails. Round cross members with a suicide front end mount.

th_DSCF4042-web.jpg th_DSCF4061-web.jpg th_DSCF4059-web.jpg th_DSCF4149-web.jpg

Note: both of these frames were for extremely low channeled cars. Both used the same reenforcement trick for the side rails: i.e. they have been "skinned" with .010" styrene sheet to smooth out the finish and to strengthen the simple butt joints used at the frame "z".

Edited by Bernard Kron

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Highboy application - AMT '29 Ford shell on Deuce rails. Stock Revell '32 Ford side rails trimmed at the rear end. Rear kickup and crossmember fabricated from round rod with suicide rear spring mount. Center and front crossmembers built from styrene "L", "T' and channel shaped stock.

th_DSCF7172-web.jpg th_DSCF7307-web.jpg th_DSCF7305-web.jpg th_DSCF7432-web.jpg

th_DSCF7327-web.jpg th_DSCF7320-web.jpg th_DSCF7311-web.jpg

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AMT Fiat Altered. Main frame fabricated from round stock. Roll bar setup from AMT Double Dragster kit.

th_DSCF0885-web.jpg th_DSCF0890-web.jpgth_DSCF1191-web.jpg th_DSCF0919-web.jpg th_DSCF0923-web.jpgth_DSCF0924-web.jpg

Edited by Bernard Kron

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Vintage dry lakes modified with simple rail frame made from styrene strip with Revell Ford Model A rear crossmember and suicide front end.

th_DSCF9178--b-web.jpg th_DSCF9150-web.jpg th_DSCF9161-web.jpg th_DSCF9164-web.jpg th_DSCF9079-web.jpg th_DSCF9076-web.jpgth_DSCF9084-WEB.jpg th_DSCF9087-WEB.jpg

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those are some great pics to get some ideas from. I am going to be building a street rod (body undecided as of now) that is powered by a Lamborghini V12. Will more than likely be using a front axle from a t-bucket kit and rear end from my parts box (or semi truck rear w/ dual wheels) and probably alot of scratch built parts. I am wanting it to look like something that could be done in 1:1 if for some reason you had the funds and just wanted something different. I haven't found the body I am going to use yet, so can't do any planning as to shape of frame needed. I am just getting pieces together at the moment. I would like for the frame to be mostly covered except for the front end which will be open wheeled...I am planning on trying to find the semi rear end and use the dual wheels, but also have several sets of pro-street wheels/tires I might use. I am always looking for pictures of different types of frames, running gear, body mounting, ladder bar/ torsion bar set ups, etc...This will be my first scratch build and just going to go all out with it.

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I bought some C channel styrene for my first scratchbuilt frame,but haven't had a chance to get started on it yet. I'm planning on building a chassis for a '29 Ford body that I have. I'm thinking the C channel will look more like a real frame,but I don't know how strong it will be. That will be the only drawback to it. I'll know once I get started on it,but have no idea when that will be.

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Roger,

The C Channel is very thin and doesn't present any simple glue surfaces, which may make it tricky to handle. Once glued together it should be pretty strong, though. Strip would be simpler for a first attempt and offer greater flexibility.

Edited by Bernard Kron

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Went ahead and got the rectangle styrene strip for frame rails and the round rod for cross members and braces. Now just on to finding a body lol...thanks for all the info and suggestions..

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