Technical Machinists, I've got a measurement question - new studs in 40 Ford hubs

I need to press new wheel studs into a cast iron hub. I need to drill the existing hole larger, but what size to use is the question. The new stud (different than the original studs) has a knurl with 0.623" OD, so what size drill would be recommended? How much press fit undersize is the norm?

The Dorman page of the catalog I found the stud on didn't have any recommendations.

My buddy with the mill who will drill the holes says he commonly uses a hammer to remove and replace the studs in the stock car axles he works on. But I thought maybe something more like a light press would be appropriate. What do you experts recommend?

 

Generally for a press fit in steel - the rule usually is .001" per inch.
So I would go .0006" under what you want.
Using a drill would be fruitless, to hit that size exactly. Find or have made a custom reamer.
Good luck.

 

I did that once, I tried to hunt down the recommended 39/64" drill bit for a .014" interference fit but couldn't find one. Used a 19/32" instead (that I could find, but it wasn't easy), ended up carefully enlarging the holes with a file slightly, and it took a fairly heavy press to get 'em in... I filed a light 'taper' so they would start easier, tried to leave the side of the hole that the stud protruded from the same. It worked out....

 

I'm not a machinist, and I'm certainly not an expert, but in my opinion, a hammer is not the proper tool for that job. I agree that a press would be the tool of choice. I raised hell at a local tire shop when a "technician" used a hammer to remove a broken stud on my daughter's car. The manager reprimanded the "technician", and instructed him to use their press.

 

Tom, those figures are for use with a knurl, or smooth shank?

 

I replaced the metric studs for standard in the new hubs for the IRS in my 67 Nova (I know, both OT), I used a 1/64 (.0156) smaller drill bit, many times they will cut a few thousandths over but one key to holding drill dimensions is making sure the drill bit is sharpened with the cutting edges equal to the drill bits' centerline
It's not always the quickest route but at a minimum a drill press should be used (not a hand drill) to hold hole size and straightness.

 

yep.
drill bits are not precise in their results. they almost always go a tiny bit oversize.
What I have done in the past is to drill, then find out that the fit is still a little tight.... good,.... then I have very lightly taken the raised knurls over to a belt sander, then carefully rotate the stud to lightly rub down only just the highest peaks on the knurl but still keep the knurl and interference fit.
That has worked perfectly in the past to make the press-fit just right as long as the metal removed wasnt extreme due to a bad choice of drill size.
I don't hammer. Too easy to warp or damage. Press with a good support under...

WHY BE ORDINARY ?

 

I'm going to go with the 39/64. Which I would think your machinist buddy already has. But if not any machine supply should have them or online seller. Perhaps you could measure the studs you removed and the existing holes and determine the interference from them

 

I would assume that it may make a difference if your pressing into cast iron or steel too...

 

These are 1940 Ford hubs which came originally with smooth sided studs that were swedged on the topside to hold the drum. My replacement studs will not be swedged, the knurl should hold them tight, and the new drum will just slide on.

 

Did the same into some 48 hubs ,,for the 0.623 spline I used a 21/32 drill,,I did a test run on a similar thickness plate ,,it worked ok with a small press ,,

 

.623 (5/8")
21/32" is .656
I think you meant 19/32"

 

Custom size reams are dang spendy but you still need to know what size. For me in the past I like to measure the O.D. of the knurl, then the base size of the shank. Pre drill to or just under that size. Then set my adjustable Ream to cut a finish hole half the depth of the spline and always press the studs in with a backer on the plate to the face side of the hub. So far, so good.
The Wizzard

 

You could drill it to within a 1/64" undersize with fractional drills, then ream it to the exact size you want for a press fit, reamers are available in high speed steel from McMaster-Carr page # 2486 their catalog # 122 ( phone 630-833-0300) in .0001" increments.
high speed is just the name of the type of material they are made from, that doesn't mean you should turn them fast.
They should be turned nice and slow in a drill press, with cutting oil. If the chips are too hot to hold in your hand, that means you are turning the reamer at too much rpm, and will result in dulling the cutting edge.

 

Made mine .005/.003 under the knurl diameter for new Dorman studs by boring to final size.
I think this falls in line with ARP recommenations for cast iron or steel hubs.
They recommend .007 interference for aluminum hubs.

No need for a HEAVY press fit, all you're trying to do is keep the studs IN and prevent turning; which is not that difficult.
This is where a little Loctite 609 can be very helpful.

If there are existing holes, this can be done on a drill press; making sure the spindle is lined up with the hole. There's a large selection of Decimal & Metric reamers to choose from at MSC's online "book"
They also have adjustable-end reamers, but these are meant for slight variations.

If new holes, best to do it on a milling machine with DRO.
A rotary table on a mill will work too, but I always felt more comfortable with DROs

 

I've redrilled lots of hubs for different studs. I shoot for .010-.015 under what the knurl mics. .010-.012 is about perfect, .015 will feel a little tight. In this case, I would use a 39/64ths drill bit, and as others have said, check the first hole to make sure the drill bit is properly sharpened and drilling close to size. As always, use a center drill and maybe even a 1/4" pilot drill to keep the size and location accurate. Lightly countersink the holes to remove sharp edges. I grease up a stack of 3 or 4 flat washers, and use an upside down lug nut and an air impact wrench to pull the studs in.

 

Never used a press, put in a larger id spacer or washers and pulled them in with a nut.

 

Firstly...a BFH has no place around cast iron. The axles your buddy does are STEEL. Cast iron cracks pretty easily. A press is the correct tool to use.
Second...it's easier to keep holes at nominal size if you sneak up on the diameter. Don't know how much you need to remove. Probably not a big deal in this case. Green Loctite bearing and stud mount will be your friend if the holes go a little wonky on you. Good for .010-.015 mismatch of hole sizes.

 

I have done several lug bolt ‘upgrades’ on MOPAR, Buick and late ‘40s Ford hubs. I have used .015” (as a nominal) interference fit with Dorman serrated studs, chosen for their dimensions for the specific application, In some case that required drilling to an oversize to accommodate the chosen stud. In all cases I used a press to install the stud in the hub. All have been very satisfactory in all respects.

 

Class V interference fit chart: https://www.engineersedge.com/class_v.htm

I have to make interference fits daily at work. Our software is coded to do it, but matches that chart, exactly.

 

I don't have one here at home, but Machinery's Handbook has a section of press fits for knurled studs, I would go by that and nothing else.

 

(This is in response to Gimpy’s reply......and was being composed when bobss396 posted his comments.)

I believe the interference fit dimensions given in that chart are intended for smooth bore and shaft surfaces. When talking about the relatively deep serrations in the shank of a lug stud, I don’t see how those dimensions apply. The serrations are intended to ‘bite’ into the walls of the hub hole and they will deform in the process.

When I refer to .015” fit, bear in mind that is based on the drill size used and the nominal dimension of the Dorman stud serrations, not a precision machined diameter of either component. And, I would not be surprised to find the drilled hole is slightly larger than the drill size. With serrated studs perhaps something less than .015” would be adequate, but .001” to .003” would not.

Were the studs smooth shank, like the Ford studs of the ‘40s, the dimensions would necessarily need to be accurate and be in the range the chart references.

 

If you go on the Jeg's site, some of the ARP, Mosure etc. studs show a knurl diameter and hole diameter.

 

I'd agree with Gatz that a mill with DRO would be much preferred over a drill press.

Having said that, a mill is only as good as the operator, and the fact that you friend with the mill is using a hammer for stud work makes me a bit nervous about the end result.

Maybe you can press the studs out, hand off the hubs for a ream, then press your new studs in yourself?

 

I have installed Moroso long studs in 32 and 34 Ford front hubs. The studs were made to go in Mustangs and such. Rather than enlarge the hole, I turned the knurled surface to the diameter of the old studs. If I had opened up the existing holes and the drill walked or the part moved, I would be screwed. If I went undersized on the lathe, I would just buy more studs. I ground a flat on the round head of the stud which hit a step in the hub and stopped the stud from rotating. And yes I used a hammer to knock out the old studs. Pulled in the new ones with a nut and spacer.

 

If not pressed for time, I'd use my cute little adjustable boring bar from my Unimat lathe/mill in my bigger mill and bore the holes to size at the mathmatically-correct location. I also especially like RichFox's approach of turning down the studs (a perfect job size for my Unimat) and a perfect application of "modify the cheapest part" policy. (I have a Maximat lathe / mill for the larger stuff.)

I also have a nice drill sharpening tool for as-accurate a drilled hole as that approach will allow. I need to get a press but have access to one.

Frankly, given how loose most drill presses spindles are, coupled perhaps with hand-sharpened drill bits, I shudder to consider how far off a bolt pattern might end up. When I consider the threads here about the troubles some have with out of round and non-concentric tires, and occasionally funky rims, I want to make sure from the get-go that my lug patterns are highly accurate.

 

Whichever way you go, a test hole as mentioned above sounds prudent.

 

Another thing. You or someone may want to put the hub back to original at some time. Drill the holes out and you are stuck with what you have. Modify the studs and you can always sell the hubs to a restorer or something if you upgrade.

 

Thanks all who have replied so far.

My machinist friend is a 50 year veteran of the machining trade, so that is why he asked me about the tolerance we needed. He did not want to guess at this because he is a perfectionist. He is very experienced at the operation to get the hole to the correct size, once we know what that is. He will index off each existing hole on the mill to center the new upsized bit.

I am guessing the reason he has used a hammer to replace the studs in the rearend of his stock car is because he knew the axle flange would be lucky to survive one season, and he said they were a half inch thick anyways. Neither he nor I would use just a hammer to remove or replace studs in these thin cast iron 40 Ford hubs.

The consensus so far ranges from 0.010 to 0.015 undersize. Anybody have an good reason not to use these figures.

 

about .010 to .015 is what i have always used