Does anyone sell a fixture for drilling broken exhaust studs

[john walker's workshop]

it absolutely has to self center over the stud and allow the stud to be drilled dead center. i'll take a steel one if it works out.

[A Quiet Boom]

Originally posted by john walker's workshop
it absolutely has to self center over the stud and allow the stud to be drilled dead center. i'll take a steel one if it works out.

That's the plan. I figure with two points (the port and the opposing stud) I should be able to line up right over the stud. Then a small insert would be installed to drill the center of the stud and then a larger insert to drill the minor diameter of the thread. Again larger to remove the threads entirely if necessary, and possibly then drill for a helicoil or timecert. I don't know if I can get all those sizes with a single OD but I'll try. What about lefthand bits? I've gotten lucky a few times in the past using lefthand bits to drill bolts out, sometimes they catch and loosen the bolt.

[john walker's workshop]

a left handed bit will just drill it out left handed. they don't generally come out, regardless of the method.

[A Quiet Boom]

OK,

Here's what I've come up with so far. If I go with metric inserts I'd need one bushing at 6.5mm which is 0.24mm smaller than JW's 17/64" bit. I'd bet that's probably the actual minor diameter of the thread but I'll check tommorrow in the machinists handbook. The other bushing would be 8mm, just 0.4mm smaller than the 8.4mm drill recommended for an 8x1.25 metric helicoil tap. I'd imagine that last 0.4mm could be honed out with a 8.4mm bit by hand if necessary. The bushings are from www.mcmaster.com and run about $9.50 each. They also have bits available which could be included. I'm figuring about $90 for an aluminum tool without removable center disk sized per the customer's port and about $150 for a steel tool with the disc sizes JW mentioned. Including the proper bits would raise the price by the cost of the bits plus shipping to me. I have a mcmaster account so ordering is easy for me. Drill inserts would be tight fit with a set screw to hold them and the center inserts would be through bolted for ease of manufacture (i.e. no tapping) these would also be a tight fit into the base tool.

I'm going to measure the stud spacing on my 3.0 for reference and I will make this tool as precise as possible. Option 2 would be inch sizing on the drill inserts at 3/16, 17/64 and 5/16. The 5/16 gets within 0.018" of the 8.4mm drill required for a helicoil insert.

My opinion is that inch sizing would be better since replacement bits are easier to come by. It also makes my tooling less expensive.

JW in your opinion are the sizes for the port inserts loose enough to fit all cars yet tight enough to register the bit over the center of the stud? Also do you see much variation in stud spacing or are they within say 0.002-0.005" on all cars. This is important from the standpoint of how tight I make the hole for the good stud. In an ideal world it would be dead on at 8mm but I imagine 8.5 or even 9 might be required.

[john walker's workshop]

a loose stud hole would cause an offset of the bushing on the other side. a 17/64 bushing with an OD of .502 was used in mine. the extra .002 would be the interference fit in a mill bored .500 hole. should be easy to get. the discs are a light tap fit in the ports. again, any extra play would reduce the precision of the tool. for now, maybe keep it simple and just use one 17/64 bushing. they need to be tight so they don't turn, so swapable bushings would be a bad idea IMHO. you could always build to order, with whatever bushing they want, 17/64, or whatever the timesert size is.

[A Quiet Boom]

JW, a bad idea even with a set screw to lock them in place? As for the stud hole, my thoughts are right at 8mm and let the buyer ream it if necessary. Would it be better to offer a third option using all three port sizes in 3 different tools and just one set screw lock bushing? See if I machine the port insert as part of the tool their is even less chance of error. Or a fourth option, two tools each having a bushing pressed in, one at 17/64 and the other at 8.4 for a helicoil. Also I assume its OK to just shape the outside the same as a gasket.

[john walker's workshop]

gasket size probably would not allow enough, or any material around the bushing. if the slip in bushings fit their bore with a no slop fit, a setscrew would probably work. the bushings would need either a flat spot, or a dimple for best results, and to keep them from spinning and ruining the bore. a setscrew would not get much of a grip on the rounded surface of a hardened bushing. nothing wrong with 3 different tools with different size integral center discs, except cost, if a shop wanted all three. i bet there are very few shops that have something like this, so if advertized, it would be a good seller. it should be heavy duty, precision and long lasting.

[A Quiet Boom]

John, what I'm thinking from a machining standpoint is that an intergral disc is much cheaper to produce, the cost could reflect this. I figured $90 for a single aluminum tool with 2 inserts. I could probably sell a set of three with single pressed in bushings for somewhere between $150-175. It's really that much simple to produce. By going with pressed in bushings it removes a drilling and tapping cycle and the integral disc removes a whole bunch of other close tolerance work. I'd make them out of steel in the three sizes, press in the bushings and ship them. This way customers could also buy just the one they need. An optional version would have removeable inserts like you decribe for those wanting to timecert the head. I didn't drive the car today (cold and rainy), do you happen to know the center to center distance of the studs?

[john walker's workshop]

66mm. derived from measuring the solid part of the stud shank on the outside between the two studs, then the inside, subtracting one from the other to get the difference and adding 1/2 the difference to the inside measurement.

[A Quiet Boom]

Thanks JW. I've got most of the code written for the CNC. Tommorrow I need to get a few endmills and a holder to make this, hopefully they'll be in stock. I currently don't have a small enough endmill and holder to do this the easy way. I'm going to start out simple with the integral disc and 17/64 drill insert. I'll have a real price for one and a deal on a set after I figure out the machine time. It's all sort of rough right now since I'm still writing code (almost typed this with the caps lock on LOL). I wish I had my new controller installed so I could just dump this from a CAM program. Unfortunately the Boss 5 controller only does circles in quadrants but they measure in within 0.001-0.002" so it's not bad, with the new controller circles should be less than 0.001" tolerance. I'm going to hand ream the 0.500" bore for the insert to insure a press fit. If all goes well I'll be making chips on friday night.

[A Quiet Boom]

Progress!

I got part of the code written last night and just couldn't resist the urge to try it even though I'm waiting on the right stock and a smaller endmill (tommorrow hopefully). The pictures show the basic outling of the part but it's not cut all the way through because the stock is too thick. I figure I'll finish the code tonight and test it all out with good stock and the right tool tommorrow. I've got enough bushings coming in to do 5 tools at first so I'll offer to those that said they wanted one in this thread first.

[john walker's workshop]

cool. if i had a mill, i'd be dangerous.

[RoninLB]

Originally posted by john walker's workshop

cool. if i had a mill, i'd be dangerous.

ditto

[A Quiet Boom]

Funny, the guys at work offer to dial 91 whenever I'm going to run a machine of some kind. That's just 91 so all they have to do is dial the other 1 LOL. Apparently Ron, has photoshop though. Thanks for lightening the pic, I'm too lazy I guess

Just got done writing what should be the last of the code for this part. If all goes well my tools and steel will be in tomorrow and I can test it. BTW that wood under the piece is walnut, I use it to test before commiting to metal. Don't get panicked though, it's some warped scrap my father gave me that won't fit through his planer. It's kind neat watching it cut wood and I don't ruin any tools in the process. I figure when this small supply runs out I'll get some machinable plastic or something. That's all for now, I'll post pics of tommorrows progress tommorrow night.

[TurboBert]

Looking good. I'll take a set if they fit a 930.

[A Quiet Boom]

Originally posted by TurboBert
Looking good. I'll take a set if they fit a 930.

I know for a fact that the studs and stud spacing are the same dimensions. I'll have to find out what the port size is. You're on the list.

I'm going to make 5 of each size as soon as I get the first good prototype done. Then I can just fill the orders for you guys. The steel is relatively inexpensive, it's mainly the time in setting up the machine and writing the proper code. Actual machining time isn't all that long either.

[RoninLB]

Originally posted by A Quiet Boom

BTW that wood under the piece is walnut, I use it to test before commiting to metal. It's kind neat watching it cut wood

walnut.. I love walnut. I love walnut gun checkering, like on shotgun grips. Why not figure out how you can gun checker the walnut? Why not figure out if you can gun checker those air cleaner housings your designing for all the carb guys? That would be so mean looking imo. Not meaning pretty, just mechanically healthy. That would be so cool with a gun checkered top with an opening for a gun checkered 2.7 surrounded by a polished flat mirror. I Need one of those.

huh

fwiw.. the wood panel is teak and the bow tie is gun checkering. Super dupper custom and tons of hours in hand carving, teak prep after each file pass, and fitting.

[A Quiet Boom]

Ron,

I'm not sure what you mean by gun checkering, do you have a closeup pic so I can get an idea? Don't know about mirror finishes, I'm not that good yet

Aluminum for two carb tops is here tommorrow. I had to pay top dollar from www.mcmaster.com because my regular metals supplier is out of stock and I want to work this weekend. I did speak to him about buying a quantity and price breaks etc.

I can't wait to get the new controller installed for the mill, the filesize for this darn tool is right near the max for the current controls at just under 4K. I'll bet I need it to do the bottom part of the air filters with all the detail work I'm putting in.

[RoninLB]

Originally posted by A Quiet Boom

Ron, I'm not sure what you mean by gun checkering, do you have a closeup pic so I can get an idea? Don't know about mirror finishes, I'm not that good yet

I'll worry about the mirror finish.

Gunstock Checkering is carving what looks like half a diamond as hand grips. You'd have to see a gun up close for a correct eyeball understanding of "half a diamond". I couldn't find my text for a close pic of the "diamond"


fwiw.. the carb filter housing site and some trick pics of Chris's machinery is CNC "watershields" my latest project.

I did a google for "gunstock checkering" and stole these pics.

[pwd72s]

Gun checkering...enables bloody, wet hands to get a better grip on the stock. Similar markings work well on tools. I love the way snap-on checkers the shaft on extensions...