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Learning how to build Lotus Seven replicas...together!
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PostPosted: October 9, 2021, 10:38 am 
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Very cool! :cheers: Care to share about your CNC router? Commercial or homebuilt, style, number of axis, etc.?

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PostPosted: October 9, 2021, 4:56 pm 
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Hi Ron,

The unit is a router/engraver that we imported about 8 years ago from a hong kong dealer who sourced it from mainland china - https://salecnc.com/product/cnc-router- ... lx-machine.

Working volume is 600mm x 800mm x 200mm.

It was cheap enough to be worth a punt, as I was originally going to build one from scratch but economics did not work compared to getting it from China. Turned out to be an OK deal, once I replaced a few of the axis bearings that seized very early on. It's really only good for cutting air as the gantry rigidity is extremely poor and it struggles on anything other than foam. For the second set of MDF dummy wheels I used my drill and jigsaw. For the foam though it works very well if the cutters are sharp. I have had great success with the Onsrud foam cutters, others tend to cog and ball very easily - YMMV. At the time of order you could buy a Z axis extension, but I see that's not listed anymore. We also added a 4th axis but never fitted it as still have not had a job that requires it. The spindle is actually a really good unit. It is water cooled, so I put a garbage bin filled with water behind the machine and have the hoses running through the lid to the fishpond circulating pump sitting inside the bin - running temps have never been an issue as it is so lightly loaded cutting foam. Accuracy and repeatability are very good though on foam. The cutting paths are created in Fusion 360 and posted to Mach 3 (which is running on an old XP desktop with serial port to the machine).

Would I repeat the exercise? No. Plan is to build a bigger unit to suit body panel scale after the track mule is running - making big parts in small sections is OK but would prefer to set it up and leave it running lights out. Researching UCCNC currently but that phase of the project is years away - only used this engraver/router to make the rear panel plug so that I have a representative piece to show family and friends who have heard me talking about doing this car for 25 years.

:cheers:


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PostPosted: October 9, 2021, 8:27 pm 
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Location: Pelham, NH
Kinetic Research wrote:
Steering - Porsche 911 rack - its the only "road car" sourced rack that has a central perpendicular pinion that I have found - although it is too narrow as stock so jury is out on how to modifiy it to make the front suspension work without bump steer.

Ohh, that sounds exciting for my project (not yet posted, in my signature). I'm having difficulty finding the width, what is it?

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PostPosted: October 9, 2021, 11:02 pm 
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If you're looking to get rid of the larger step patterns that occur on steep surfaces, just do another mill path 90 degrees (x or y) to the previous mill direction. Use a "steep" or other control to limit it to the steep parts. Or use line geometry to "fence" it in. If those aren't options, just remill the whole thing at 90 degrees.

I've had good luck with taking a "spade" type drill bit and hand shaping/sharpening it to a BEM shape.

LinuxCNC is free, you still need stepper/servo drivers.

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PostPosted: October 10, 2021, 12:33 am 
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Darxus wrote:
Kinetic Research wrote:
Steering - Porsche 911 rack - its the only "road car" sourced rack that has a central perpendicular pinion that I have found - although it is too narrow as stock so jury is out on how to modifiy it to make the front suspension work without bump steer.

Ohh, that sounds exciting for my project (not yet posted, in my signature). I'm having difficulty finding the width, what is it?



I will measure the length of the rack for you, it's buried away under some other parts but will dig it out and post the a pic with dims. My approved design now requires a bespoke rack from Titan motorsport in the UK. The setup of the suspension on the build table will prove out the bump steer and define the width of rack I need to order but am using the 911 rack as a dummy for the mock ups.


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PostPosted: October 14, 2021, 3:18 pm 
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Attachment:
rear panel foams.jpg
rear panel foams.jpg [ 322.73 KiB | Viewed 1054 times ]


Have the next few project days booked out for gluing, sanding, bogging, sanding, glass and epoxy laminating, bogging, sanding and more sanding before applying the final epoxy seal coat. Then more sanding and priming, then sanding and priming again. At that point I will be thoroughly sick of sanding but ready to apply release to the plug and make a tool from it. The plug is in 3 main sections to allow adjustment for the build up of the outer skin thickness and the opposing polyester shrinkage factor (1mm/m), which I have no experience with, however I have found the most practical way to get something right first time is to do it a couple of times beforehand.


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PostPosted: October 14, 2021, 10:32 pm 
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Kinetic Research wrote:
........however I have found the most practical way to get something right first time is to do it a couple of times beforehand.

Ha Ha Ha Ha Ha I love that saying, how true :cheers:

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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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Perry's 5th Build, the Super Slant Six 7


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PostPosted: October 22, 2021, 8:56 pm 
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After a few hours of assessing various alternatives decided my favourite tune to sand the plug to is "smack my bitch up" by The Prodigy.

Glued the patterns to an MDF backboard with the raw epoxy resin, it gave plenty of working time to position the parts carefully. 24hrs later applied a thin layer of epoxy & West System 410 filler mixed to a peanut butter consistency, however its a bit like putting the crumb coat of icing on a cake, the thick sticky paste peels off the foam underneath all too easily, very frustrating but overcome by applying lots of patience. The epoxy is really good to work with though as there is no time pressure forced by a short cure window. 24hrs later sand back, blow down and repeat. 24hrs later, sand back, blow down and add the fairing layer. Once the fairing layer is cured will be adding all the little corner details and both side panels. Then it will be ready for epoxy and 200g glass cloth.

Attachment:
surface prep.jpg
surface prep.jpg [ 217.62 KiB | Viewed 851 times ]


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PostPosted: October 30, 2021, 1:36 am 
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Added a stout wooden frame behind the mdf backing sheet since the plug needs to be transportable in a trailer so that I can get it painted in a spray booth. Will brace it with flat bar once all the glue has cured.

Surface is almost ready for glassing once the side panels are blended in. Overall the faces have enough draft to release, but the rear vent slots still need a lot of work to ensure they don't key the mold in place.

Surprised at how exothermic epoxy is even only 25mm deep, wasted a small pot due to taking too long on the alignment of the sides panels, by the time I got back to the pot to mix in some filler it was almost fully cured and REALLY hot. Cheap lesson that I do not want to repeat.

Attachment:
rear curves.jpg
rear curves.jpg [ 110.63 KiB | Viewed 649 times ]

Attachment:
rear quarter.jpg
rear quarter.jpg [ 164.48 KiB | Viewed 649 times ]

Attachment:
side pattern.jpg
side pattern.jpg [ 71.42 KiB | Viewed 649 times ]


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PostPosted: October 30, 2021, 7:12 pm 
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Kinetic Research wrote:
Surprised at how exothermic epoxy is even only 25mm deep, wasted a small pot due to taking too long on the alignment of the sides panels, by the time I got back to the pot to mix in some filler it was almost fully cured and REALLY hot.

Building airplanes, (1 full size and too many RC to count), I've used 5 minute, 15 minute, 30 minute, and 2 hr epoxy.
Epoxy sets slower spread out on a pallette than in a pot.
Ambient temp and surface temp plays a big part in set time.
The longer the set time the stronger the bond.

Looking forward to your end result on this BTW, great build.

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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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PostPosted: October 31, 2021, 5:46 am 
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Thanks Perry!

Put the Kutzall ball into the drill to blend the corners, holy crap it was like trying to strangle a rabid beaver that is jacked up on methamphetamine! Does the business on anything it touches, chews through the wood very quickly and given the chance would eat a big hole in flesh instantly.

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PostPosted: October 31, 2021, 8:54 am 
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Use an oscillating palm sander (five inch or so) with hook and loop/velcro 320 pad to rough.
This is standard autobody repair shop equipment except for being electric versus pneumatic.

Works great polishing aluminum with finer grits.
Made for what you are trying to do.
Much better and easier than using a drill with a disc arbor.

If you ever need to shape soft foam for upholstery, a radial wire brush in a drill works great but takes a lot of dexterity and two arm support, barely touching the foam or it will rip out chunks.

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PostPosted: November 7, 2021, 3:34 am 
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While waiting for epoxy to cure cut down some cap heads screws and barstock on the lathe to create the pivot axes for the rear suspension control arms, once positioned on the build table will be measuring the bump steer characteristics and adjusting positions of everything so that it is minimised. Each knee as shown weighs 40kg.
Attachment:
control arm axes.jpg
control arm axes.jpg [ 174 KiB | Viewed 388 times ]


The devil is in the detailing, was concerned with the glass cloth not conforming to the sharp edges so have stepped back the edges of the 8 vent slots and will form the small radii with filler instead. Risk is the edge might come away with the mold when it is pulled but will be easy to sand out if required.
Attachment:
final detailing.jpg
final detailing.jpg [ 196.45 KiB | Viewed 388 times ]


To achieve a 3 degree draft angle on all internal faces I ground the edge of my bog spreader and radiused the corner, with the left edge flat against the backplane the tool formed the correct draft when held perpendicular to the wall.
Attachment:
draft tool.jpg
draft tool.jpg [ 21.42 KiB | Viewed 388 times ]


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PostPosted: November 7, 2021, 8:31 am 
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Kinetic Research wrote:

concerned with the glass cloth not conforming to the sharp edges


Use a "285" designation weave for extra conformity for whatever material you decide to use. It is also called "crows foot" with a distinctive weave pattern that makes identification easy. More layers of lighter weight cloth versus fewer layers of heavier cloth helps too. You could just use layers of 285 around the problem areas to sandwich with more typical weaves or use 3 layers of 285 then back with microspheres/glass beads or cotton fibers/flox and resin to level the problem followed by standard weaves or mat. If you intend to vacuum bag, it can still be a problem with corners.

Don't fret about any tiny bubbles you may end up with. Air pockets are a problem IF they can get filled with water and freeze.

If doing this yourself, I suggest making something small beginning to end, like a mail box.

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My posts are my own opinion and do not represent an official public position by any other person, place, thing, animal, vegetable, mineral, etc.
https://www.azsenaterepublicans.com/audit
https://www.oann.com/india-govt-declares-most-populated-state-officially-covid-free-after-widespread-use-of-ivermectin/
https://www.oann.com/fauci-hhs-officials-discuss-using-new-virus-from-china-to-enforce-universal-vaccines-in-footage-from-oct-2019/
https://www.oann.com/the-story-of-iverm ... -the-drug/
https://pubmed.ncbi.nlm.nih.gov/33278625/
https://rumble.com/vokrf7-sen.-johnson-expert-panel-on-federal-vaccine-mandates.html


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PostPosted: November 7, 2021, 11:41 pm 
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Great suggestions MV8, thanks. Will ask at my fibreglass supplier.


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