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Building a Pre-Add BRM

12K views 81 replies 18 participants last post by  Rail Racer 
#1 ·
The combination of an apparent high level of interest in Mac Pinches Pre-Add bdies as decribed in "News" and the recent arrival of some of Mac's new laser cut chassis has prompted me to start another project along side the W154/Patto chassis that is ongoing.

Thinking that there might be some interest in this project, I am going to document it in photos and (hopefully) brief text as it progress.

These will be a series of "real time" progress reports, not a "how to" since what I describe in one post may well be reversed in the next when I discover that it didn't work! I'll try to keep a rough log of time and cost.

The bits and pieces:


In no particular order: the body molding, driver, vac-formed screen and metal castings for the steering wheel, exhausts and filler cap (all part of the body kit) There are actually two chassis in the picture - on the lower right the laser cut chassis as supplied and spread about the middle, the parts after cutting and removal of the webs. The rear axle carriers/rear motor mount are "stuck" together. The fit of the parts is so good that the assembly is stable without soldering! Also in the picture is a guide and guide shaft bearing. One of the first things that I do with any commercial chassis is to try and figure out what guide shaft fits the hole. This is of particular interest for laser cut steel chassis because my experience is that these holes can oly be enlarged with some difficulty, the steel being very hard. In this case, the TSRF guide made for conversion of plastic chassis is a perfect fit and, on preliminary examination, to be short enough so that it will not extend beyond the front of the car (important for some rules)

Now let's do the numbers: A quick Google search yielded:

http://8w.forix.com/brmp15.html

LOA: 158"
Width 56"
Height 35"
WB 98"
Wheels and tires: 5.25 X 18 front, 7.00 X 17 rear

If I believe my digital caliper, the wheelbase is spot on and the length is very close (perhaps 0.10" too short, but, the body that Mac has modeled differs from the one pictured on the site so I'm going to call it perfect!

A listing of tire dimensions for Dunlop Vintage Series tires yields:

7.00 X 17 30.2" diameter
5.50 X 18 30.1" and 5.00 X 19 29.6" so I'm calling 5.25 X 18 as 29.7"

This translates into 0.94" rear tires and , rounded to /100s, the same at the front.

Quick dimension check: The distace from the center of the rear axle carrier to the bottom of the chassis is about 0.288" If we subtract that from the radius of the proposed rear tire, 0.47", we are left with 0.18", plenty of room to add a weight pan and still meet a 0.125" ground clearance rule.

Second check - height is listed @ 35" or 1.1" in 1/32 scale. Knowing the axle height we can then check the body to see where the axle would be to give us that height in the finished car - and it turns out to be exacltly where Mac has placed the top of the rear axle slots!

Little worry (postponed until the initial chassis assembly is done and a motor fitted) - the fit between the top of the motor and the dash is the limiting factor for positioning the body on the chassis and, at first glance, it is a problem. The decision will be: can enough be ground off the bottom of the dash to accomodate the motor or will the dimensions dictate a front motor placement (and, in the latter case, isn't it nice that the chassis kit includes twoadditional motor mounts!)

An issue which has arisen long before its time: decoration: I am not really enamored of the peculiar diseased liver green that was chosen for these cars! (I recognize that there may have been budget constraints but did they really have to use paint left over from the redecoration of the railway station loos?) Any suggestions as to alternate correct liveries will be appreciated. I reserve the right to assign the car to Ecurie Martini and since this organization (long predating the red, white and blue "Martini" sponsorships) is a Belgian/American consortium, I'll paint it yellow!

Time so far, hands on and on the net, about 2 hours - parts @ current exchange, about $50

Next steps: chassis assembly, motor, axles & gears

EM
 
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Discussion starter · #7 ·
Next steps: Warm up the soldering iron. It's a real treat to work with well made parts. Everything fits together perfectly - no hammering, bending or colorful language! The various pieces have reasonably large fastening surfaces so I decided that a high strength soft solder would be sufficient. I like "Tix" - it has a low melting point but is very strong. Stay-brite is also good. Contrary to some opinions, i think that steel is esier to solder than brass with the right solder and flux (acid). It is a poor conductor of heat so the heat stays were you put it, the joint region heats up fast and neighboring joints are not disturbed. I also believe is big irons. Most people use 60-75 watt pencil irons. Unless the space is too small to accomodate it, I use a 150 watt truncheon with a pyramid tip - when I want hot, Ii get hot! here's the result -still needs a good scrubbing and sanding:


Dead easy - just tin one of the surfaces, apply flux, put the parts togethr and heat. the parts fit so well that you don't need 4 arms to keep everything in alignment.

After attaching the rear axle carrier/motor mount, I soldered in a pair of bronze bushings so that I could get an accurate position for the rear axle to double check the wheelbase. The Pre-Add chassis offers 6 wheelbases by using 3 different postions on front axle carriers that can be installed in 2 ways. The BRM wheelbase is 98" or 3.0625" in 1/32. I found two choices: 2.96" and 3.205" (these are rough measurements made by eyeballing axle centers and lining up the points of a dial caliper) I chose to go 0.010" undersize and fitted a length of 1/8" OD brass tubing to the appropriate holes and soldered in the front axle carriers followed by the guide plate which fits between them and finally, the bushing for the guide.

A little grinding and the chassis dropped into the body:


Then the TSRF guide was "offered up" Ah, well, so much for eyeball estimates - the guide extends beyond the nose by 1/16" or more and that will get worse with braids installed:


Back to the parts bin...after all, it is and ordinary 1/8" post - and here's an MRRC one:


Now, I have not had the best of results with these guides but perhaps it is just a matter of learing - decision pending (do I want to try for the race win or the concours win?)

And, thanking people for their suggestions:

QUOTE And I think the duck egg blue is great

Is it really blue - the pictures I have all look to be very pale green I could live with a light blue.

QUOTE An alternative to the er.. pee green could be the dark green as run from late 1952 and into 1953?

Did the P 15 run under those colors or was it a later version?

chassis soldering - 30 minutes
body grinding and fitting - 45 minutes
pondering the guide problem -I hour!

To be continued......

EM
 
Discussion starter · #14 ·
QUOTE and NO! im not going to take a wife to help out

Odd, my feeling is that if I didn't have one, I might make more rapid progress!

QUOTE a thing i have found with the chassis, if you take a little metal from the side uprights that fit into the base of the chassis, this gives for and aft movement of these uprights thus allowing the chassis to be used for other cars macp

Very good point - I simply didn't think of that!

No progress last night - wine tasting dinner - head should be clear by about noon.

Next steps involve another dive into the parts bin: First thing to address is the "BRM sound" - and the fact that I think a fair bit of weight will be needed to keep things upright so my first try will be one of Patto's "Little Rippers", reputed to be good for 37,000 RPM, geared about 4.5:1 to both handle the weight and provide some brakes. Because of the rear wheel dimensions, this will be similar to about a 3.8:1 gearing in a model of a current car.

EM
 
And now the tale of a couple of 180 degree turns (If anyone went out and ordered parts on the basis of my last post - I warned you at the outset)

Time to fit a motor: With the guide problem semi-solved, my next concern was the clearance between the motor and the dash (fascia across the water) In went a standard FK can (TSRF, Little Ripper, Cheetah, Fox etc.) and into the body. As I expected it hit the dash. Burr in the Dremel and grind away - but how much? I made the decision that I would not cut beyond the point of the preformed hole for the steering wheel. Cut and try again- the chassis still would not fit all the way into the body. 3 choices:
1. Cut more and glue the steering wheel to the top of the motor - not acceptable
2. Go to a front-mounted motor - good choice but not for this project - only as a last resort if there is no alternative
3. Different motor - I have an assortment of mini-motors but while poking through the parts boxes, I took out an SCX motor - it is 0.56" high vs the 0.6+ of the FK can - enough to make a difference - take a look:


40/1000" is just enough! Here is the motor mounted:


The installation is not without some problems:The contour of the can is different from the FK (a bit wider at the flats) requiring that the inner upper coners of the chassis rails be filed a bit. The shaft-end stamping of the SCX motor is not exactly a precision part and when mounted with the single available screw hole (note- drill an additional hole in the next chasssis while it is still in the flat), the bottom is "pulled" and the motor slopes down towards the front. This cannot be corrected by installing the front motor mount . the chassis simply flexes. One could solder the motor in but I was unwilling to do that at this stage. - Solution - a high tech shim (folded decal backing stock) at the lower edge of the motor mount:


With this in place, the front motor mount was set and soldered.

So, the idea of a high revving motor with short gearing has gone by the board - and, as it turns out, just as well. When I began to fit the gearset, I immediatley realized that the spacing between the axle carriers was too narrow for any of my 64dp metal gears! They all have an external (opposite the gear teeth) hub in contrast to the typical plastic crown which has an internal hub. I fitted a Slot-It 3:1 gearset. These are nice gears, perhaps the best of the molded plastic but my prejudice is that a well bedded 64dp metal set is smoother and more durable. Does anyone make metal crown gears with an internal hub?

With one exception, the rest of the project should be simple plug and chug. The exception: wheels and tires.

The P 15 mounted 17" wheels at the rear and 18" wheels at the front. Nothing in my parts bin nor on any of the web sites I visited had an acceptable combination of diameter and width. I do have some 60's 1/24 wheels that are close but they are all made for threaded axles and boring and bushing them is a fiddly task that I have never done right. The simple answer is to chuck up the aluminum bar and turn away but I am going to try an alternate approach. A 17" wheel will have an outer rim diameter of 19-20" or about 0.62" in 1/32 scale. The diameter of the ridge of the BWA wheels is 0.62" and, the really hard work, getting a round OD and a concentric, square bore, is already done so I shall machine off the outer rim of a wide BWA wheel, cut a tire depression and drill and tap the inner rim (AKA the brake drum) for a 1-72 set screw so I can glue the tire on and true is prior to mounting - like this:


The broad dashed line defines the area to be removed, the dotted line the tire recess and the little bulls-eye the location of the new fixing screw. I think I can find a suitable Ortmann tire - probably a narrow 1/24 front - to get me to the desired 0.97" tire diameter.

The fronts are still "under review" I am thinking about simply turning the whole business out of delrin -light, easy to turn and perhaps the characteristic clatter of hard wheels on a track will offer a simulation of bits and pieces falling off, rods exiting crankcase etc. I have also picked up some O-rings with a 3/16" section and want to see how they will look mounted with the outer surface gound flat.

The best laid plans...........

EM

About 2 hours of fiddling around
 
Discussion starter · #24 ·
Almost rolling: The next logical step was wheels and tires - I like to have those set before I do the body mounts - measuring and calculating is fine but, in the end, I want to see what it looks like!

I decided to take a shortcut and modify some BWA wheels I had on hand. Here's the before and after:



For those interested in the process: I mount a wheel on a piece of 3/32 drill blank and chuck it in a 3/32 collet then face off the front back to the edge of the rib. The depression for the tire is then machined - I used a 60 degree indexable carbide tool perpendicular to the work giving me a 30 degree angle on either side. The wheel front is then hogged out with a 5/16" end mill mounted in the tailstock (could go larger but that is all the chuck will handle. The recess is then finished with a boring bar to a 0.505" ID to suit cut-down Ninco wires as inserts. (I run the boring bar in until I hit the set screw - this messes up the screw and threaded hole but this is not a problem since I subsequently cross-drill the brake drum to take a 1-72 set screw. This allows me to glue the tire on and true it without worrying about access to the mounting screw) The wheel is removed and the axle pushed thru to allow it to be mounted backwards. The rear section was turned down to 0.44" - to make a 14" brake drum. there was a fair amount of back and forth on the dimesions of the wheel, mounting and unmounting various tires until I got the "look" that I wanted:



From left to right: two rear wheels with Ortman 1/32 tires mounted, one cndidate front with and EJ's #15 tire and at far right, the same wheel with a 3/16" cross section O-ring mounted and grond down to provide a flat tread ( More about the O-rings later)

The difference in width is apparent:



Again, left to right: Ortmann, EJ (rounded), O-ring

And finally -



AlFin drums, of course!

The O rings are an experiment - perhaps a bit too rounded for anything later than about 1950 but pretty good earlier than that and, I think, better than most choices for 30's and earlier. They are available in a vast range of cross sections and diameters in fractional inch, decimal inch and metric measurements. I have no idea if they offer any traction at all - not a concern for fronts - but I shall see if they can be coated with RTV silicone such as Permatex Form-A-Gasket to serve as rears as well. In addition to the size range, they offer another advantage - they are about $6.00 for a bag of 50!

Now that I have wheel dimensions, I can cut the axles and front bearing tube to length and get things rolling.

Time - about 2 hours to figure out the first wheel and tire set-up - 20 minutes each to do the rest

Costs: 2 pr BWA wheels @ $6.50/pr, set of Ninco wheels - about $5.00, Ortmann & EJs tires - $10 - axles $1.00 (I buy ground drill blanks in lots of 25 from an industrial supply house)

Looks like it's going to be about a $90-$100 slot car

EM
 
I have been using diamond disks that I get from Micro Mark.

http://www.ares-server.com/Ares/Ares.asp?M...roduct&ID=82259

They are thinner, cut cleaner and cooler and seem to last a long time. You can also use them (carefully) side-on to clean up the ends of the webs left after cutting the chassis apart. An alternative approach to drilling the guide tongue for the Sakatsu guide would be to substitute a piece of brass of the appropriate width with the 3/16" hole drilled in it. I think it would be easier than drilling the existing guide and you could leave enough metal around the hole to stabilize the guide.

Good luck - and show us how it comes out!

EM
 
Discussion starter · #31 ·
QUOTE Why not bring it to the NLondon retro in May?

I was about to reply that a transatlantic trip to a slot car meet might have certain domestic repercussions when it occured to me that I will, indeed, be in the U.K. in May.
what is the date?

EM
 
Discussion starter · #34 ·
QUOTE Why not bring it to the NLondon retro in May?

Won't work for my schedule - I'm there 11-14 and the schedule is not mine to control. But what is the meet about - assuming that the car survives the Las Vegas bash, I could send it across. Is it a race? (The last time I sent cars to race in England was in 1962 - the Whitehaven GP - two cars, both with Braverman bodies and Pittman motors running on SMEC rubber - a bit overpowered!)

EM
 
Discussion starter · #37 ·
QUOTE How did your cars perform in the 62 race?

Well - memory fades so one goes back to the sources - It was the 1961 race! - and only one of my two cars, a Birdcage Maserati, was a Braverman body - the other was a home built glass Vanwall (both bodies survive in reasonable condition)

Quoting from the October 1961 issue of Model Maker, p 562:

"Laurie (Cranshaw) then got down to adjustng all of his proxies, Braverman's proving not the least difficult. Like the other U.S.A. entries this had fixed steering, which whilst being extremely fast down the straight, were sliding back ends really wide in the corners."

This is not surprizing. I was using a motor about equivalent to a DC 62A driving SMEC wheels and tires!

Apparently a series of heats were run, with cars assigned by some mechanism to a lane (and not rotated) Somehow, four finalist were chosen from among the (I assume) winners of the heats to compete for the honors. Evidently it was assumed by the writer of the article that everyone was familiar with the procedure - it was not explained.

My Maserati finished second in its heat with 19 laps to the winners 20. The Vanwall finished less well at 15 laps to the winners 20 although the winner of that heat posted the fastest time and was the eventual overall winner.

A side note: At the time of the race, I was engaged to be married to a young lady who lived in Perkasie, PA. Sellersville, the then home of Pittman motors was the next town. I visited the Pittman factory and met Mr. Pittman, working at his stand-up desk. I showed him what I had done with some motors spirited out of the locomotives from my now supplanted HO guage system as well as my adaptation of the DC 703 to a side winder configuartion in Merit cars. Several weeks later I received a package containing two motors with integral brass axle carriers and pinion and contrate gears and having the brush gear mounted on the side of the motor (as in the DC62A/B). He asked for my evaluation. I believe that these were the first slot car motors that Pittman made. They were used to power my entrants. Like the bodies, they survive today.

EM
 
Discussion starter · #47 ·
We're rolling! the chassis that is:



The axles are cut to length (although with a 52" front track and a 51" rear track, perhaps I should say that they are cut to "shortness") In the foreground is the rough-out 0.063" brass weight plate.

The body mounts used the two centerline holes provided in the chassis. I have a "formula" body mount - thusly: pieces of 3/8" hollow plastic tube are cut well overlength to fit between the chassis and the inside of the body. Knurled brass 2-56 inserts are pressed into one end of each tube (I ease them in with a warm soldering iron - never had one pull out) They are bolted to the chassis and the body set on top. the overlength tubes are ground and filed down until the body resets at the correct height. In the end stages, I try to shape the tops of the tubes to fit the contours of the insdie of the body. When I am satisfied with the fit and convinced that the body will rest squarely on the tubes, I put a dollop of 5 minute epoxy on the top of each post, position the body and go away for a while. When the epoxy has set, I carefully undo the bolts (the post/body joint may be weak) and then reinforce that joint with gussets of 0.063" styrene sheet set in place with high viscosity gap-filling CYA

All that done - the question is now - do we have the right "look?" - The overall impression from photographs is of a very low car (35") with rear tires reaching the base of the headrest fairing and fronts that are just slightly above the body line:



The TSRF guide, forward protrusion aside, is a near perfect fit. The MRRC guide will need to be machined down to get it low enough to fit under the nose.

Paint shop time - Bowing to tradition, I have ordered some Duck Egg Blue (Humbrol) with Floquil Polly-S Sky Type S as a back-up. While waiting for the paint, and then waiting for the paint to dry, next steps include finishing the weight plate, glueing and truing the tires and fitting the wheel inserts. I have a bit of travelling to do so there will be about a one week hiatus

EM
 
Discussion starter · #51 ·
I get my inserts, along with a lot of other supplies and tools, from McMaster - Carr (this is a U.S. firm)

http://www.mcmaster.com

They are certainly not the cheapest but their stock is enourmous and delivery is typically "next day"

I am sure that there are metric and BA equivalents ex-US - you just need to find a good mill supply house.

-and thanks for the compliment - it has been a pretty straightforward project so far thats to the quality of Mac's parts.

EM
 
Progress: Very little - and the reasons why:

The little progress - The correct shade of paint is now in hand and painting will commence as soon as I decide if I am going to further grind the front part of the body to model the trailing arm front suspension -

The reason for the lack of progress:



Didn't finish particulary well - guide kept coming out of the slot on the windward leg.

EM
 
Discussion starter · #59 ·
Well - we are moving along albeit slowly - there is this expression: "the Devil is in the details" - and so it turns out.

After looking at photos of the real car and, in view of the fact that the "ears" on the chassis offered a perfect mounting spot., I decided to add the trailing arm front suspension. the suspension bit was easy - a little cutting, filing and folding of a short piece of rectangular brass tubing - 1/8" hole on the outboard end to fit over the axle tube and a bit of solder at the inboard end to hold it to the chassis:



The tinned brass was painted with Humbrol burnishable steel and the axle tube got a coat of invisibility paint ( aka flat black)

AS in the prototype, a considerable opening in the body is needed:



And now the fun begins - first, the body seemed a bit flimsy after all that material had been removed so I elected to reinforce the upper part of the body/nose with several layers of kevlar scrim set in epoxy - glass fibre, carbon fiber, or even old nylon stocking material (the latter set in airplane dope) would do as well.

That done, I did a trial assembly at which point it became painfully obvious that the front body mount was off center by about 1mm - the plain axles sticking out each side had been less revealing. No way to fudge that much so - grind it out and make a new one - about half an hour + overnite drying time that was unplanned.

Having come this far, there was nothing to do but add the trailing links for the rear suspension - easy - a little recess in the body, two hole for two bits of wire etc. Here's the result of the third attempt to get the "little recess in the body" right:



With, of course, the requisite body filler application, setting time, sanding and repriming following the first and second attempts! Is is not perfect, but it is done!

My driver figures have never been very good, at least in part becaise they are always the last (and rushed) thing that I do so I decided that this one will be different- some scrapng to creat the "bare arm" polo shirt uniform that will go with the brown leather helmet and a lot of fiddly heating (butane cigarette lighter) and twisting of arms and hands got me to here:



With the wheel installed, he is held forward a bit and grips the rim quite convincingly - and yes, the wheel really does stick up that far!

Tomorrrow should see the first coat of color (then 24 hrs - then the secnd coat then 24 hours then the first gloss coat etc. etc) and while all that drying time is elapsing, I'll finish the weight pan.

Next post should be the finished car ( I hope)

EM
 
Discussion starter · #62 ·
Almost there - but I thought that i would post a few shots while waiting for the driver to recover from tapping the hole for the #2 X 1/4" screw that will fasten him to the seat ( Ferrari isn't the only one that can..........)

The body is painted - 3 coats of Floquil "Sky type S" - I know that the Humbrol "Duck Egg Blue" would be more appropriate, it being a British car and all but the redoubtable Prof. Fate has assured me that they are the same color and Floquil is available locally while Humbrol is a 'net purchase with various vendors demanding from $7.50 to $10.00 " S/H" to deliver a $1.49 tin of paint! The exhaust pipes are painted with Humbrol polished steel metallizer - very nice- goes on flat but will burnish to a very convincing mettalic lustre - a few minor details to catch up with but here are the key bits ready for assembly:



The ballast plate is 0.063" brass. As I described earlier, the chassis will "float" between the ballast plate and the body thanks to shouldered nylon bushings.

A close crop is a really harsh way to look at one's handiwork:



One of the details that remains is a bit of Bare Metal Foil on the mirrors - I pulled mine out last night and - no adhesion at all - I didn't realize that the stuff expired until I read a bit in the instructions about keeping it sealed in plastic under refrigeration! The dash is covered with matte metal foil and the instruments as decals made by Virage (France) that I can find only at Slot32.

For comparison:



There are obvious differences in body shape. Based on what I have gleaned from my "Google research" the pictured prototype is the first body and Mac has modelled a later version. I don't put much stock in the color difference. The downloaded photo looks too "warm" to me. Other pictures suggest that the model color is pretty close.

Next time it will be really finished, I promise.

EM
 
Discussion starter · #65 ·
QUOTE I have gone a different path with the chassis. Made mine front engined. Hope it works!!

A front-engined version of the Pre-Add chassis is on my "to do" list - but I'd love to see how you implemented it - any chance of a picture?

Thanks

EM
 
Discussion starter · #73 ·
Wrap -up time! Although there are still a few little bits to look to - Bare Metal Foil for the mirrors - final guide adjustment (the car has not seen the track yet) the project has moved from the workbench to the "ready for Las Vegas" staging area:







A thinner braid should bring the front down when combined with the 0.010" recess of the braid on the Las Vegas tracks but I may still substitute the MRRC guide if I get it re-done in time.

For comparison:



Adding the BRM to the other ~ 1950 GP car in the stable:





I'm hoping to at least make a sandwich of Larry LS' Talbot!

This has been an interesting exercise - the first time in 60 years that I have built a model with someone(s) "looking over my shoulder " as it were.

And now the bottom line:

I probably have about 30 hours in the whole project including perhaps 4 hours invested in pictures, processing and publishing. The biggest single time element of the project was shaping and painting the driver - took seemingly forever with at least 4 re-do's. But I learned a good deal in the process which will make the next round a lot easier.

Adding it up:

Body & Chassis: $60.00 (at current FX)
BWA wheels 13.00 ( 2 Pr)
Rear tires 6.50
Front tires 2.25
Motor 11.75
Gear set 8.00
Guide 2.50
Misc 10.00 (paint, adhesives, wire, brass plate and tube etc)
Total: $114.00

Now, is that expensive for a slot car? - not as I see it:

It works out this way - 30 hours of amusement and relaxation for $114 - that's only $ 3.80/ hour - pretty cheap - and then I get my ego massaged - many thanks for all of the lovely comments and the inspiration - so, after this bargain basement indulgence, I get a nice little slot car for free!

EM

"The night has been long, ditto, ditto my song, and thank goodness they're both of them over" - Iolanthe
 
Discussion starter · #78 ·
QUOTE I assume you'll be keeping us posted in a similar way as you work through the rest of MacP's catalogue?

Certainly, albeit perhaps not in such detail - The underpinnings of the 4.5 Ferrari have been posted on the "Geddes Joint" thread. Currently underway - a W-125 on a Patto stainless steel chassis - schedule on that is a little uncertain as I am now in my usual "why didn't I start sooner" panic before the early May Las Vegas event with promises to prep at least 3 cars that aren't even started yet! - but , of course, I have most of Mac's newest enroute. He has warned me that the current chassis is too long to fit the later cars but we shall see.

And thanks very much for your kind comments

EM

PS - I have had several conversations with Al Penrose ( Mr. BWA) and I have every reason to believe that tall, narrow wheels such as those needed for the older cars will be forthcoming - and that will greatly simplify things.
 
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