By Matthew Harwood – Harwood Performance USA
Like many of you, I looked
all over the Internet for pricing and designs, and found a lot of options, from
nice professional units to really cobbled-up amateur units that I wouldn't use
to rotate my lawn mower. I also work in a machine shop that uses A LOT
of steel--there are literally tons of steel sitting just 50 feet from my desk.
I also need to practice my welding. Between those easy facts and the idea that
I believe I can build a better rotisserie for less money, I set out to design
my own.
Here's
some of the steel in Mustang's warehouse. Plenty for a small job like a
rotisserie. They can even cut it for me.
The
first fault I've seen on a lot of rotisseries out there is that they are either
too narrow or the wheels are placed in such a way as to make them the most
vulnerable area for breakage. I plan to roll this thing around, and even up
onto a trailer to take the body to the sandblaster and painter, so it has to
have good, solid wheels. With certain wheel outrigger designs, I also think
there will be too much flex, making it difficult to really put force into what
I'm doing on the car without it wobbling around. I wanted to start with a solid
foundation.
The
second fault I've seen is inadequate tubing size. Yes, I know I over-engineer
everything I do, but for something that is potentially going to support several
thousand pounds in a variety of different positions that move the center of
gravity around, I decided that bigger is better. Most rotisseries I've seen use
2" square tubing, which looks kind of spindly. Some designs add small
corner gussets made from plate steel, but unless they are substantially taller
than those I've seen, they're pretty useless in preventing flex. My design
remedies that problem, too.
Initially,
I wanted to use 4” square, ¼” wall tubing, but the price of steel being what it
is makes that cost-prohibitive (that first design required over $800 in
steel!). Instead, all of the tubing on my rotisserie will be 3/16” wall
thickness, and range from 3” square down to 2” square along with some 3” x 2”
rectangular tubing. The sizes I've chosen are common and easy to find, and will
fit together without much extra effort. That really helps during assembly,
especially since there are several slip joints and pivots on the thing.
The
third fault is height and center of gravity problems. A rotisserie has to be
high enough to fully rotate a car body, but not so high that it becomes
top-heavy. This situation is exacerbated by wheels bolted under the braces or
to the ends of the braces, which tends to raise the center of gravity. I
designed my wheels to be "under slung" On a flat concrete or asphalt
floor, ground clearance is not an issue.
Finally,
there's tying the two ends together. Some do, some don't. I don't like the idea
of the body being used as a structural part of the assembly. This can lead to
some twisting or torque that can easily be prevented by running a beam between
the stands. Again, I'm using thick steel here to make it as rigid as possible.
One
feature I often see is height adjustability on the main upright using a
hydraulic jack system. While this seems like a good idea in theory, it's
important to remember that unless the centers of rotation on each end are on
the exact same axis, the thing won't rotate very well. That's why I've left my
rotation pins in fixed locations on the uprights and instead built the height
adjustability into the brackets that actually attach to the car. With this
setup, different heights between the front and rear of the body can be accommodated
without affecting ease of rotation. I'll also add a pair of grease nipples in
the pivot sleeve to keep it lubricated and easy to move.
To
make my design strong, all the joints must be welded. Unfortunately, that means
that my rotisserie will not be very portable, and with the thick steel, it'll
be heavy. On the positive side, adapters can easily be made to convert it into
a pair of heavy-duty engine or transmission or differential stands. I think
that's a fair trade-off for strength.
I
also had one of the structural engineers here at the shop take a look at my
plans and materials. He ran a stress analysis on it and said that it should be
good to at least 2268 kilograms, probably more. The casters I've spec'd are
rated for 363 kilograms each, and there are 4 on each stand. I could probably
rotate a complete car on this rotisserie, though I can't imagine why I'd want
to. Still, it never hurts to have capacity you won't use, right?
Here's
the complete materials list: This list is in Imperial. The RHS thickness can be
changed to suit your need.
On
the upcoming pages, I'll take you step by step through the construction and
show you how I do it. I think it's the best design out there and plenty strong
for any car you're likely to be working on.
I
laid out all the parts and made sure I actually ordered the right stuff. It
looks like I got everything. The guys at work even labeled each part for
me--nice! Thanks, Eser & everyone else in the Mustang shop.
It's all here; the guys in the shop even labelled each
part for me.
Compare to the pieces in the materials list above
The
first thing I did was start to clean up the ends of the steel where it had been
cut. The rough edges would not only be difficult to weld satisfactorily, but
were as sharp as razors. I used a sanding wheel on my die grinder to knock off
the mill scale and rough edges so the surfaces would be clean. On pieces where
the ends would be welded, I bevelled the edges of the tubing so that I could
get more weld surface area. One of the most important things I've learned about
welding is that it is all about surface area. On structural welds in thick
steel, it is critical to have enough metal to make several passes to get
complete coverage and penetration, especially with a smaller welder like mine.
Bevelled
edges improve weld quality.
I
laid out the main "T" of the base and shimmed it so that the pieces
met perfectly square to each other, then tacked them together. I'm going to
tack the whole assembly together so I can make any last-minute adjustments to
the plan, then finish weld all the joints later.
I welded the
main "T" together first.
You'll
notice in the photo above that the top joint is fully welded. That's because I
noticed the upright would cover the joint completely, and I wouldn't be able to
get full penetration with the weld if I covered it up. So I did a triple pass
weld and finished it. I ground it smooth with the die grinder so that the
upright would fit flush. This is another important tip for welding: make sure
you can get full penetration before you cover any joints with another piece of
metal.
The quality of my welds has definitely improved. They
need to be
as good as I can make them for this project. This is a triple-pass joint.
Adding
the upright was easy. I positioned it and used a level to make sure it was
straight and a metal ruler to make sure that it was flush with the base
"T" then tacked it in place as well. This steel is heavy enough and
thick enough that I don't really have to worry about the weld
"pulling" the part as I would when welding lighter parts. Pulling is
when you're tacking one side of a part and the other side separates because of
the heat.
Tacking
the upright in place.
Attaching
the outriggers for the rear wheels was next. These joints need to be very
strong since they'll be carrying all the weight of the assembly. Fortunately,
these welds will be very strong because of the rounded corners of the tubing
which makes a perfect trough for multiple passes with the welder. It should be
plenty strong once it's all said and done. I just tacked them in place for now,
however.
Outriggers
tacked in place. On a structure like this, it is critical
to get a good weld on every single surface you
can reach.
Next,
I tacked the diagonal braces into place. With the 45 degree cuts on these
braces, the relative square ness of your base will be immediately evident. If
the braces don't line up on the upright, it isn't square. Fortunately, mine
lined up perfectly, a testament to taking your time and making things right
before you do any final welding.
All 3
diagonal braces meet at the same height, indicating that the
upright is perfectly square to
the base.
The
next step is probably the most difficult part of the whole job: cutting the
"cradle" that the rotating sleeve fits in. I used my Sawzall to trim
it close and finished it with a cylindrical die grinder bit. It is important to
note that if you're using my design, carefully locate the rotating sleeve--it
isn't quite half-way set into the upright, so don't make your cut too deep.
Make it too shallow and gradually widen it with the die grinder to make a
perfect fit.
Carefully cut your cradle area. Note that the cradle
is not quite equal to the radius of the rotating sleeve.
Before
I tacked the sleeve in place, I placed a level on the base and levelled it
using a few small pieces of sheet metal. Once the base was level, I placed the
level on the sleeve, levelled it and tacked it in place. Why is it so important
to make sure everything is level? Since the sleeves on each end need to be on
exactly the same plane, any tilt to it will induce bind into the apparatus. If
there is any bind, it could add some torsional stress to the body once it is in
place and make it more difficult to rotate. Making it as perfect as possible
will give you a better chance of avoiding problems (this is a lesson
well-learned in my days as a carpenter).
Once
everything was where I wanted it, I set the entire assembly up on a makeshift
welding table I set up in the shop. When doing any finish welding, I find it
easier to position the work where I can make a flat weld at a comfortable
level. Kneeling on a floor trying to make a weld work on a vertical surface is
no way to get strong welds.
Setting
work up at a comfortable level leads to quality welds.
Welding
thick metal is going to be a challenge with any "hobby" level welder,
mine included. Though it says that it will weld ¼” metal, it won't do it for
long without overheating, so plan your welds accordingly and don't just keep
going--make sure you pause occasionally to let the welder cool off. I typically
put my tack welds in the middle of joints, then finish weld on each side to
minimize the time I spend with the welder going full tilt.
With
such heavy metal, it isn't so critical to prevent heat build-up as it is with
sheet metal, but if you are doing finish welds on one side of a piece with only
a tack on the other, it is possible to pull the tack apart with the heat. Use
caution and common sense.
My weld quality has
definitely improved. Though this is kind
of a crappy photo, this is a near-perfect "stack of nickels"
joint
with excellent penetration and coverage.
Another
decent weld. Corners are thicker because of passes
from each side and the back overlapping.
I
ran into a problem when I went to build the rotating assembly, specifically the
pin that fits inside the sleeve.
When
I bought the round tubing, the pin fit inside the sleeve easily. I believe the
heat of welding must have distorted the sleeve to the point where the pin would
not fit inside. I spent four days trying various ways of enlarging the sleeve,
ranging from a cylinder hone to a sandpaper wheel to a diamond-tipped die
grinder bit I borrowed from work. No dice. I couldn't believe how much the
sleeve had changed size! Ultimately, I took the pins to work and had the guys
in the machine shop take 0.030" off of each pin on the lathe. Result: perfect
fit with a great surface for retaining lubricant grease.
Turning
the pin diameter down slightly
made it fit perfectly in the
sleeve.
I
also used the sandpaper roll I purchased yesterday to smooth out the inner
surfaces of the rotator sleeve to help it rotate properly. It left a really
nice, smooth surface.
Inside of rotator sleeve
is smoothed to help make rotation easier. Also
note
the hole for the grease fitting.
Then
I drilled a hole on each side of the sleeve, one in front and one in the rear
to supply grease to the rotating assembly. I tapped the hole to accept a grease
nipple Overkill? Perhaps. But that's the way I do it.
I
did make one addition to the blueprint of the rotisserie, and that is a pair of
triangular gussets that hold the rotating sleeve to the height-adjustment
sleeve. I thought about how the round tubing was welded to the square tubing of
the height-adjustment sleeve, and figured that some additional support would be
a good idea, especially since I'd made the pin thinner by turning it on the
lathe. Stronger is better in this case.
I'll be
adding some triangular gussets between the round tubing and
the square height-adjustment sleeve
(vertical piece on the right).
I
ran into another problem. Despite three engineers plus countless well-wishers
taking a look at my design, nobody noticed the one critical flaw:
I think
the picture speaks for itself...
So
I did the only thing I could: cut the forward brace off. I'll do a slight
redesign on the forward brace and replace it with some gussets made from ½”
plate.
The fix is in.
I
also built the body bracket and drilled the height adjuster to hang it in place
(which is how I found about the interference problem). I had so carefully
designed the thing to clear the front diagonal brace, even at its lowest
position, but didn't stop to think about what happened when it rotates. Duh.
I
also added a collar and small gussets around the adjustment sleeve to keep it
aligned and strong. The collar should also help retain the grease in the
rotating mechanism. I'll add a second collar at the back that will be retained
by set screws or a pin.
Collar
and gussets.
I'll
drill two mounting holes on each side of the adjuster sleeve to hold the body
brace in place. My thought is to drill the holes in the body bracket at the
appropriate heights for the Buick. In this way I can custom fit it to the car.
Future projects will have their own holes drilled--the steel will be plenty
strong to accommodate several sets of holes, and they may link at a variety of
different heights in the future. I feel that since I'm not building a
production line item and probably won't be restoring dozens of cars (or
maybe...), putting a hole every two inches, for instance, probably wouldn't be
as helpful.
For
drilling the holes, I've found it's better to put the sleeve and the body
bracket together at the appropriate height, clamp them in place, then drill
through all four walls at once so they line up perfectly. Take your time with
the drill--use a low speed and lots of lubricant (WD-40 or cutting fluid) and
steady pressure. A drill press is ideal, but you can do it with a hand drill if
you're careful.
I've
solved the clearance issue by using 1/2” plate steel gussets instead of the
diagonal tubular brace (I'll be updating the blueprint to reflect this change).
However, I had to make an executive decision regarding strength vs. range of
motion and chose to go with strength. While there is undoubtedly much more
clearance for the rotisserie to rotate using a gusset instead of a brace, it
isn't perfect. In order to clear the body brace completely at its lowest
position, the gusset would have been much too small to do any good against
flex. So I decided that the rotisserie will rarely, if ever, be used at its
lowest position, at least not for rotating, and made the gusset large enough to
handle whatever loads I throw at it.
Plate
steel gusset does the job just fine.
I
also added gussets to the body bracket's "T" area. Since this will be
holding a majority of the car's weight, sometimes at an angle, I thought it
important to make it as strong as possible. Again, the scrap bin at work was
invaluable for providing perfectly-sized scraps of triangular ½” plate.
Triangular
gussets add strength without taking up too
much space on the horizontal bar.
I'm
picking up the casters tomorrow and hope to have at least one complete unit ready
for paint this weekend or next week. This one is close while the other still
needs some final welding and sizing on the rotating sleeve.
Fixture one is almost
finished.
We're
in the home stretch now. I finished all the welding, attached the wheels, added
a few gussets here and there, and drilled a lot of holes for adjusting the fit
and angle. I used a drill press to accurately drill some holes in the rotator
pin for locking it in position. I also added quite a few "lock bolts"
in the pin, the height adjuster and the body mounting brackets. While I don't
trust these bolts alone to hold the body in position, they can certainly
supplement the pins I'll be adding and will hold it in position while the pins
are installed. Properly tightened, they seem to hold everything very solidly.
Consider the pins safety insurance.
I
drilled holes in the rotator pin for a pin to hold it at 0, 45 and 90 degrees.
Use a
drill press for this process to ensure straight holes that line up properly.
Also
note the welded nuts for the "lock bolts"
Finished
stand. Cosmo (black) and Lily (with scarf) liked to be
Around
during welding, so I had to be careful to lock them up whenever
I struck a spark to protect their eyes.
Remember this if you have kids or pets...
Then
I painted the stands. I prepped the surfaces by sanding them with my DA sander,
and then wiped it down with solvent to eliminate any oils or leftover WD-40
from the drilling processes. I used the same Rustoleum epoxy I used on the buffer
stand. You'll also note that I brushed it on--after finding out what a hassle
the paint gun is to clean, I'm not really in the mood to use it unless
absolutely necessary. I think it looks pretty good nonetheless...
Looks
good in black, doesn't it?
It's
finally finished! I added a few features at the last minute that I thought
would be helpful in the future, such as lock bolts for the brace between the
tripods to hold the brace solidly rigid. I also finished painting the thing,
which is no small feat considering every time I put a coat of paint on
anything, it falls over, bugs land it in, Julia decides to use the leaf blower
to clean the driveway, whatever. I'll let the photos speak for themselves.
Finished product. Though
there is only 1 bar between the tripods, I have two with a sleeve to join
them in
the middle to accommodate various size vehicle bodies.
Finished Rotator Sleeve
Arrow A: Retaining ring with set screw to hold
pin in sleeve
Arrow B: Lock bolt to prevent
rotation (safety first!)
Arrow C: Lock pin for safety (will be replaced
with actual pin instead of bolt)
Arrow D: Grease fitting
Judging
by the amount of E-mail I get about it, and from the response to the
plans being posted at autobody101.com, a lot of you are wondering about
my rotisserie. Wonder no more--it works perfectly!
Tonight
I put the Buick up on the rotisserie. The process was quite easy--I bolted the
body braces to the body using fender washers to space the body off the braces
to prevent damage. Then I slid the braces into position on the tripod and
locked it all down. Using a floor jack on each side of the body dolly's side
rails, I jacked up the body about 6 inches and secured the height adjusters in
place. Lowering the jacks allowed me to roll the body dolly out from under the
body and it was on the rotisserie. Easy.
Body
was easy to mount on the rotisserie. I still have to cut the tie-bar
to length so I
can fit it between the tripods to join them together.
When
I tried to rotate it, it moved easily--even Julia could rotate it. The catch
was that my garage ceiling isn't high enough to allow it to rotate even 45
degrees. So I rolled it outside, taking advantage of a 60-degree evening (in
January! in Cleveland!). Moving it was easy, and the tripods rolled easily as I
expected. I need a few adjustments--the body mount up front hits the very end
of the tripod; I need another inch of clearance there, so I'll redrill the
mounting holes in the front body brackets and give myself some more room. I'll
also move the rear tripod closer to the body by again drilling more holes in
the brackets. Otherwise, the whole assembly won't fit in my garage. Still, with
the height problems of my garage ceiling, I'll never be able to move it 90
degrees indoors, so it will have to be done outside. Nevertheless, I can still
do a lot of work underneath with it at about 40 degrees.
Rotisserie
rotates, but the body is just too big for my garage. A little
adjustment to the body brackets will give me
enough clearance to
rotate it 45 degrees (arrow).
Body rotates effortlessly. Note how rear brackets
are bolted to the body.
I locked the rotisserie in
position and crawled around underneath, checking out my earlier floor repairs.
I plan on dressing all the welds to make the repairs invisible, and the
rotisserie will make that easier. I think the first thing I'll do, however, is
send it to the sandblaster's place and get it all stripped down. There's still
a lot of rust and even the patches I've made have some surface rust. I'd rather
have it stripped then I'll treat the whole thing with Picklex-20 to prevent
additional rust while I work on it.
Easy access to the underside. My
new floor brace is
in place, but the welds need some attention. I also
need
to spot-weld the brace to the floor and repair the
holes.
And in case you don't want
to take my word for how well the rotisserie works, here's one built by a
reader, Rick Doritty. He's restoring a Camaro using a modified version of my
design. It turned out well. Thanks for the photos, Rick!
Rick Doritty's rotisserie. Nice!
A
huge Thanks to Matthew Harwood for permission to use this article from
his site
Disclaimer:
The advice and guidelines given in these articles are given in good faith.
The owners and managers of the Galeforce Zephyr site will take no
responsibility for any injuries or loss sustained while carrying out the
described tasks and procedures or any consequences arising. Please read
the Safety First
Article