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 Post subject: Error Tolerance?
PostPosted: November 28, 2020, 9:55 pm 
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Joined: November 6, 2020, 6:29 pm
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Location: Spring, TX
How much margin of error is acceptable when it comes to the angle cuts for the frame? +/- 1°? More/less?

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 Post subject: Re: Error Tolerance?
PostPosted: November 29, 2020, 8:48 am 
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Joined: September 22, 2005, 8:12 am
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Location: 4AGE in S.E. Michigan
The angle can be off several degrees, it's the weld gap you should be concerned about. Probably most builders will start to have problems filling in a gap of much more then .030" on a fit-up using thin wall tubes and slightly larger gap on the heavier gauge brackets. You can move the tubes slightly to improve fit-up plus grind or file the tube ends to improve the fit-up. That being said, you should try to dimensionally get everything set correctly, which will make placing the suspension brackets i.e. pivot points spot on, after completing the frame. Frames are alter all the time, what really counts is your suspension system. You need to clamp your tubes in place, then tack weld them, to hold their location. DO NOT try to complete any weld(s) with a free standing tube or bracket. The weld will shrink and dimensionally f#$@yu.
Finally if you do have a tube out of location, you will not be the first one to have to cut it out, and replace it. Down the road it will make the build a lot easier. davew


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 Post subject: Re: Error Tolerance?
PostPosted: November 30, 2020, 5:05 pm 
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Joined: November 6, 2020, 6:29 pm
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Location: Spring, TX
Thanks, that puts my mind at ease a bit.

I was considering sourcing the frame/chassis metal from a place that could cut to spec. But if it's more error tolerant than I was expecting, I imagine it would be significantly cheaper to buy the steel in larger lengths & DIY the cuts. Will have to call them & see the difference.

If a big price gap, then off to figure out if my miter saw is sufficient (with proper blade/disc), or if I should look into a more metal oriented cutting tool.

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 Post subject: Re: Error Tolerance?
PostPosted: November 30, 2020, 6:43 pm 
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Joined: August 28, 2010, 7:53 am
Posts: 298
Check out the Evolution Rage saws
They are awesome! They make fast accurate cuts. They cut so well that the part doesn't get very hot

https://www.amazon.com/Evolution-Power- ... 12&sr=8-17

When building the chassis, always use the same points as a reference so you dont accumulate error. I made the chassis side rails VERY parallel and the firewall perpendicular to them, and used them as the master reference. It is worth taking the time to make it accurate, because it makes building the rest of the car easier.


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 Post subject: Re: Error Tolerance?
PostPosted: November 30, 2020, 8:35 pm 
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Joined: October 24, 2008, 2:13 pm
Posts: 4626
Location: Carlsbad, California, USA
JAMADOR wrote:
Thanks, that puts my mind at ease a bit.

I was considering sourcing the frame/chassis metal from a place that could cut to spec. But if it's more error tolerant than I was expecting, I imagine it would be significantly cheaper to buy the steel in larger lengths & DIY the cuts. Will have to call them & see the difference.

If a big price gap, then off to figure out if my miter saw is sufficient (with proper blade/disc), or if I should look into a more metal oriented cutting tool.


Let me give you some reassurance about accuracy. Here is a Locost {scroll down half page} whose chassis was cut entirely by hand with a hacksaw. I've seen it in person. It is a really nice build. It was not his first Locost, but I think it's more about attitude and taking care. I guess you could call it craftsmanship.

I bought an inexpensive Harbor Freight metal cutting bandsaw, but part way through building my chassis bought a freestanding, traditional metal cutting bandsaw because I wanted to work with irregular pieces, and improve the accuracy of my angle cuts. You don't have to do that, but I was willing to spend the money. I got lucky and found a used one on Craigslist for $500.

That said, there are other, cheaper ways to do it. You can cut the pieces slightly larger than the plans indicate and do the finish trimming to fit using hand files, or a small grinder. There is a lot of hand fitting anyway, so it's more time to do the finish work by hand, but not that much.

Last, I sold my HF bandsaw, and bought a Rage Evolution. It was mostly to save space in my garage. It's a great machine, very fast, and cuts nicely. However, it's hard to set up the angles accurately, especially on larger pieces, so you may have to do some final hand work anyway, so be prepared for that.

The initial task is going from long lengths (10 or 20 feet lengths of raw steel) to chassis-sized pieces (a few inches to 36", say) then doing the fitting up. You can look at buying a portable bandsaw then buying (or building) an aftermarket platform that converts it to a stationary, table top bandsaw. You can do the initial cuts slightly oversize with a hacksaw and then do the final cuts on the converted portable, finishing the angles by hand, if required. With practice and care, you can get to any level of accuracy required for a Locost.

Said another way, there are many ways to skin this cat. Even if you're on a small budget, there is a solution.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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 Post subject: Re: Error Tolerance?
PostPosted: November 30, 2020, 9:44 pm 
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Joined: August 28, 2010, 7:53 am
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Lonnie - i keep my Rage saw at 90* and have an adjustable angle block that i clamp to the fence (a sine plate from Ebay) that i use to set angles Much quicker, easier and more accurate.


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 Post subject: Re: Error Tolerance?
PostPosted: November 30, 2020, 10:11 pm 
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Joined: March 19, 2011, 10:22 am
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Location: Holden, Alberta, Canada
All straight cuts on my band saw. All angle cuts with a sawzall free hand and dressed up with a flap disk.
The beauty of welding is that it fills the gap, which in the perfect world is what you want a weld to do for proper penetration.

I've witnessed a lot of B pressure pipe welding, the welder will gap his/her work pieces the thickness (~1/16") of a steel square so that the root weld will penetrate to the ID of the pipe. BUT the thinner the material, the smaller the gap should be.

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"No one ever told me I couldn't do it."
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Perry's Locost Super Che7enette Build
Perry's TBird Based 5.0L Super 7 L.S.O.
Perry's S10 Super 7 The 3rd
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 Post subject: Re: Error Tolerance?
PostPosted: December 1, 2020, 10:40 am 
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Joined: October 24, 2008, 2:13 pm
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Location: Carlsbad, California, USA
Sean in CT wrote:
Lonnie - i keep my Rage saw at 90* and have an adjustable angle block that i clamp to the fence (a sine plate from Ebay) that i use to set angles Much quicker, easier and more accurate.

That sounds nice, Sean. Care to post a photo here?

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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 Post subject: Re: Error Tolerance?
PostPosted: December 1, 2020, 11:14 am 
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Joined: November 6, 2020, 6:29 pm
Posts: 300
Location: Spring, TX
Thanks guys. All helpful, for sure.

I have a 3 car garage, and am fine with putting my DD in the driveway, but don't want to kick the wife out of the garage. So that leaves about 1.5 bay of space to house a donor NB Miata & a build table. The donor will fit fine where my DD sits currently & from my measuring, a build table should fit in the 3rd bay. Could them put the wife's car outside to work & give more room.

Good to know it can be done without investing in a lot of large tooling that I'm space limited to store.

I'll be making some calls today & pricing the metal, both as whole lengths & cut-to-spec.
I did some excel maths yesterday & think it comes out to about 20x 8ft 1" square & 1 1x2 piece. That should leave some extra & allow for overcutting the pieces & fine fitting afterward.
In my mind, getting 8ft lengths would be easier to pick up & transport from a supplier to home.

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 Post subject: Re: Error Tolerance?
PostPosted: December 1, 2020, 4:11 pm 
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Location: Oregon, usually
davew wrote:
...you should try to dimensionally get everything set correctly, which will make placing the suspension brackets i.e. pivot points spot on, after completing the frame.
I'm a professional parts makes, not a professional car designer, but I think the most important part of chassis straightness is, and can be achieved by, placing your front suspension hookup points on the frame based on the rear suspension hookup points. Or vise versa. The point is, your chassis is basically a large bracket holding your front and rear suspension in alignment, with additional fittings to keep the engine from falling on the ground and your butt inside the bodywork. If your suspension parts are properly located, I don't think it matters much if your chassis has minor excursions from the book dimensions in between.

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 Post subject: Re: Error Tolerance?
PostPosted: December 1, 2020, 10:04 pm 
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Joined: March 19, 2011, 10:22 am
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Location: Holden, Alberta, Canada
JackMcCornack wrote:
davew wrote:
...you should try to dimensionally get everything set correctly, which will make placing the suspension brackets i.e. pivot points spot on, after completing the frame.
I'm a professional parts makes, not a professional car designer, but I think the most important part of chassis straightness is, and can be achieved by, placing your front suspension hookup points on the frame based on the rear suspension hookup points. Or vise versa. The point is, your chassis is basically a large bracket holding your front and rear suspension in alignment, with additional fittings to keep the engine from falling on the ground and your butt inside the bodywork. If your suspension parts are properly located, I don't think it matters much if your chassis has minor excursions from the book dimensions in between.
Jack I couldn't have said it better. I've always stated that the frame is the basis to accurately locate the suspension points. If there is a bit of frame warpage or not squareness, no problem and long as the suspension points all come together properly and accurately.

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Perry

'If man built it, man can fix it'
"No one ever told me I couldn't do it."
"If you can't build it safe, don't build it."

Perry's Locost Super Che7enette Build
Perry's TBird Based 5.0L Super 7 L.S.O.
Perry's S10 Super 7 The 3rd
Perry's 4th Build, The Topolino 500 (Little Mouse) Altered
Perry's 5th Build, the Super Slant Six 7


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 Post subject: Re: Error Tolerance?
PostPosted: December 2, 2020, 8:34 am 
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Location: 4AGE in S.E. Michigan
If you are looking for an actual tolerance on suspension location, shot for +/- 2mm on pick up points for the control arms. Note: with such a low CG, front anti-dive will only be in the 1.5 to 2mm range. davew


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 Post subject: Re: Error Tolerance?
PostPosted: December 2, 2020, 11:01 am 
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Location: Carlsbad, California, USA
JAMADOR wrote:
. . . . In my mind, getting 8ft lengths would be easier to pick up & transport from a supplier to home.


The standard length for tube in the USA is 20 feet. If you cut to 8' there is going to be a short piece at 4'. Not that that's a crime, and there are plenty of places to use 4' lengths. It just limits you, and you will be charged for the additional cut at most suppliers. Two 10's is mo' betta and mo' flexible.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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 Post subject: Re: Error Tolerance?
PostPosted: December 2, 2020, 11:02 am 
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Joined: November 6, 2020, 6:29 pm
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Location: Spring, TX
Lonnie-S wrote:
JAMADOR wrote:
. . . . In my mind, getting 8ft lengths would be easier to pick up & transport from a supplier to home.


The standard length for tube in the USA is 20 feet. If you cut to 8' there is going to be a short piece at 4'. Not that that's a crime, and there are plenty of places to use 4' lengths. It just limits you, and you will be charged for the additional cut at most suppliers. Two 10's is mo' betta and mo' flexible.

Cheers,

Thanks. Will revise my 'maths'/diagrams to 10ft lengths. Not sure I could fit, nor transport, 20ft tubes.

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 Post subject: Re: Error Tolerance?
PostPosted: December 2, 2020, 12:03 pm 
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And some steel suppliers (like the one I use locally) will give one free cut per piece so you dont pay to cut 20 footers in half.

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