M20 Dreaming

[Chris Kouba]

Leonmac,

Looking at photo ...26.jpg, I had a thought. I understand if the space and packaging is a challenge but have you thought about doing your inboard pivots in double shear?

It seems like you're going through a LOT of work and adding the boss to the casting would be a good way to locate those arms.

Chris

Edit for the pic:

[Mick Ridley]

Leon,

A friend of mine on this site John Edwards, is building a alluminium honeycomb chassis, which is bonded, and rivited. He may be able to help you with the choice of adhesive.

There are some pics of his chassis, on page 3 of the chassis threads
Look for ...Chassis design using honeycomb core....

I hope this helps......

[Terry Oxandale]

Leon, I found something tonight that looked very promising, and that is 3m's VHB tape. I watched various videos demonstrating destructive testing of the tape, and was quite impressed. They have it down to a fairly thin 15 mils, but they also have what is called an "adhesive transfer" tape that is in 2, 5, and 10 mils. Very interesting stuff.

http://www.uline.com/Grp_240/3M-VHB-...FQUUswodWF-L5A

[Leon]

Chris, you bring up a good point, the Hewlands have a seperate bracket that bolts to the base of the diff case. I have thought about doing the same or making some little "L" shaped brackets that bolt on where those lugs are at present, One of the main reasons is because its hard to drill the hole for the front lug as the flange that connects the bell housing sticks out so I dilled right through it as well. As is obvious the parts are still wood and very much in the mockup stage so I appreciate any thoughts that will make the job easier. the other thing I'm trying to achieve is that if I win the lotto and can afford a LG600 that the arms,links and brackets that I make will be able to be used so I'm trying to get the locations and hole spacing the same.
Thanks for the interest.
Mickky, I have read that thread on the ally/honeycomb chassis so I will hunt it out again and have a read, Thanks.
Terry, My plan was to do the bonding with out the rivets and once the adhesive is cured then do the rivets. With the way my table is I can drill all the holes on the floor panels and use wood screw's to set it down to the table so its all square and in the correct place, use tech screw's to locate the bulkheads and the side panels then glue it all together and screw it up tight, once it is cured (I will do it before I go to work) so it will have 5 weeks to cure I can take the screws out and bang in the rivets. What do you think??? Cheers Leonmac

[Leon]

Hi Terry, we must have been writing at the same time as when I posted I saw your lastest post. I have watched the demo's and as you say the stuff is pretty impressive but it still has the "Flex" that seems to be the thorn in this disscusion. I have to say that puting the tub together with that tape would sure be a lot cleaner and easier than any apoxy or liquid glue, I wonder how it would be if riveted as well. The distortion of the panels you talked about with the glue under the rivets would be worse as I would think the glue would be thinner than the tape but it beggs the question, Do you need the rivets??? I would want the rivets for my car as it is part of the detail of the replica tub, without them it just wouldn't look right. I have to admit the tape has me thinking. Cheers Leonmac. Just a note about the dimple effect, if you look at some pictutres of riveted mono they seem to have a little of it and it just adds to the character, Thats just my thoughts.

[Jac Mac]

Leon, when you drill the rivet holes the action of drilling will creat a 'burr' at each hole & push the panel away slightly, thats why the A/C guys drill & cleco the panels, then remove & deburr before finally rivetting panels together, using threaded screws would increase the amount of 'burr' or deformation in the area.

[Leon]

Good point Jacmac, I had in tended to have all the holes predrilled before final bonding and to clean up any burring, That said would I have much of an issue with just drilling the finish hole for the rivet once the tech screw was removed bearing in mind the bonding is already done, and whats your thoughts on something like this 3M VHB tape over a liquid adhesive. I remember Leon and Russ saying how hard it was to get the panels done before the adhesive that he used went off. Cheers Leonmac

[Russ Noble]

Leon,

The Plexus is doable. The main issue with the working time is that if you spend too long fastening one panel the glue will go off in the special mixer nozzle on the gun before you move onto the next panel. Thus you need plenty of mixer nozzles. Of course you waste all the product in the mixer nozzle, but that's not a major consideration bearing in mind the overall build costs. Just goes against the grain for impoverished Kiwis!

On the issue of single shear on the lower rear suspension arms, whilst theoretically less desirable from a design viewpoint, in actual practice many single seaters and sports racing cars of that era did just that with no obvious problems.

I'm following this build with interest and really admire your efforts so far. Best of luck, I can't wait to see the mono taking shape.

[Leon]

Hi Russ, good to hear from you again, Have you been hybinating for the winter. You are of the "NO Flex" thinking I'm guessing. I think the work time was what was putting me off the most and I remembered you saying about the amount of waste if the stuff goes off in the nozzle.
As for the twin shear mounts I'm in two camps I see some merit in the fact that a single shear lug needs to be much more robust and could be seen as heavier but if you look at the uprights the joints are all single and I have no doubts about them as that is the way they were done in the day although where the top link connects to the Bracket on the G/Box it is a twin but its made of 16 gauge steel so it has to be.
If someone could show me a Photo of the bracket used on the bottom off the Hewland box's I would do it the same. Nice to hear from you Russ,
Leonmac.

[Leon]

Terry, I have been reserching the 3M VHB and I like what I'm reading, they do tapes as thin as 0.4mm Even with rivets in they would distort very little and the flex would be next to nothing, I may see if I can get a sample and do some tests on it myself as well as doing some with the Sikaflex, thanks for the info, its been well worth the discussions. Leonmac.

[Jac Mac]

Leon, cant help with the comparative properties of these sealants/tapes your discussing.
I did visit Temperos in Oamaru around 96/97 when they were building some of the XJ13's in alloy mono form [ Way before any of these johny come lately's doing them now].
I was with an aircraft engineer @ the time & we discussed the size of rivets & spacing that they were using, dont recall what or if any sealant adhesive was being used- there was no visual evidence of any, but I know my fellow SAA guys were having trouble sourcing a ' Durolac ' product at the time [ Baby Poo, as it was affectionately known!], local Mercury Marine distributor helped on that one @ about half the price of the CAA approved version..

[David Morton]

Leon,
The 3M VHB products are quite amazing. We have had similar discussions here on the web site previously. I would definitely recommend using them and I wish they had been available when I put my car together. There are various sorts of VHB and 3M have a spec sheet s for each one so you can make your choice.

[Leon]

Jacmac, I remember seeing some Jags at Tempro's around that time, they were in the workshop at the bottom of the hill as you head south out of town from memory, they are still going but long since moved shops. It does beg the question, did they use adhesives on the mono's back then?? because there certanly wasn't the flash stuff back then they have now and if they didn't that pretty much answers all the questions.
I have to say, I'm swaying to this 3M and its good to hear from people like David who sounds like he may have had some experience or Knows of the stuff being used sucessfully in these type of applications. It was when I saw how thin you can get it that made me think it could work. If it were thick ( 2mm or more) then I think there would be too much flex in it. Anybody else who has used it would be good to hear from. Cheers Leonmac

[Terry Oxandale]

It seems to me one tech sheet for adhesives I saw put the "ideal strength" bond at about 5-7 mils. In my particular case, I am going to bond (ether tape or adhesive first), then rivet. I've already drilled and cleaned the holes, so all I would need to do is Cleco a couple of pilot holes to ensure everything is lined up, clamp it all together with some angle aluminum, let set (even the tape suggests clamping and a setting time to ensure all the micro-voids are filled), and then re-clean the holes (for tape or adhesive) and rivet it.

My guess is that the adhesive transfer tape is very intolerable to even slight deviations in the flatness of your joints. So in all practicality, you may only get 50% coverage or direct bonding with this. The tape on the other hand, would have much higher tolerance for deviations in the joint, probably giving you an 80% to 100% bond depending on the quality of the joining surfaces (but it is thicker). It was interesting to note the difference in dynamic vs static loading. Between different expansion coefficients, vibration, and sealing from the elements.

It's going to be tough to decide.

[Mick Ridley]

Leon,

An ..."indication".... of the different strengths of the adhesives, "should" be possible by comparing the quoted tensile strenghts

The best tape....160psi......(1.1 mpa)

Sikaflex.............260psi.....(1.7 mpa)

Plexus MA 830...3773psi .....(26 mpa)

The Scotch Weld doesnt give a tensile strenght, but gives...overlap shear, and shear modulus........

[Terry Oxandale]

Thanks Mick. I'm guessing the tape is based on dynamic loading only because I believe the static load strength is significantly less (allows creep), where the adhesives probably have little difference between the two.

[Leon]

There is a hugh difference from the tape to the glue that is clear, I think what needs to be decided (and this will different for everyone) is what is enough?? do you need the strenght of the Glue when you have rivets every 25mm and is the the ease of the tape make it worth the sacrifice in strength, does a tiny bit of flex in the tape or the Sikaflex stop the possible cracking around folded edges and other places where the stress is trans ferred because the tub is so ridgid. and the question of wheather they used an adhesive at all is still out there. For Terry its not so bad, at the end of the day 90% of the strenght in his car is the steel tube frame and the alloy is clothing and if the frame does flex then alittle movement in the bonding might be nice. Now my head is starting to hert.

[Mick Ridley]

Leon,

Here is one to ...."mess your head up".........

The tensile strengths, of the adhesives, are between 1.1, and 26 mpa

The tensile strenght of NS4 alluminium, (a reasonable hard, and ready available alluminium), is about 200 mpa

Does the tensile strength, of the adhesive,need to be the same as the the alluminuim ?? (if it was the only way of joining the materials..ie no rivets)

I dont think so as....as there are more loadings going on, (not just loading trying to pull the materials apart)

There will be "shear loadings"on your chassis


Scotch-Weld...shear modulus......342 mpa

Plexus MA 830.....modulus........500 mpa

I dont know the answers...Im just trying to understand it.......

There are some very knowledgable people on this site..I hope they will share their knowledge with us .......

[Mick Ridley]

Leon,

I see your flanges which you will be riveting are about 25..30mm wide..

If the original chassis, had one 1 line of rivets 25mm apart, and you were to use 2 lines of rivets staggered, my guess is you wont need to bond the alluminium aswell....

There is probably a simple formula, for working out, how many and what size and strength of rivets you need to join, different thicknesses of alluminium together...at the end of the day, the joint only needs to be as strong as the materials you are joining

My nephew works at .... .Boscombe Down.. an.Aircraft, and Armament Experimental Establishment,

Let me know what grade of alluminium, and what gauge, you are useing, and ill ask him to get some answers for you



I

[Leon]

Hey guys, this has turned into the perverbial monster, and I start to think how would have Bruce and Denny done this in the 60s. My guess (being a kiwi) is they would have rang the local hardware store and said " what have you got that will glue alloy sheet" the guy would have said , Ive got this. Bruce would have then glued two bits of alloy and he and Denny would have tried to pull them apart and if it didn't break they would have said " that ill do" and built the darn car. So I wonder if we are over thinking the whole thing, I love the ideas and stuff this is bringing to the task but Are we thinking 21st centry when we need to step back 40yrs, at the end of the day the lowest grade adhesive today is still light years ahead of what was availible in 1972 and I don't see those mono's falling apart 40yrs later. So lets just run with what you brung and see what transpirers. at this point I'm 60% 3M and 40% sikaflex. As I said at the start of this debate, Someone has to be the lab rat. it may as well be me.
Cheers Leonmac