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Steel grade recommendation

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ecdez

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#1
I have a small production run of specialized gear pullers I'd like to make and one of the parts I'd like to do on my turret lathe. The part looks like the item blow. I could just buy the "bolt" but then it wouldn't be made by me and the cost of the bolt would push me too close to my target sell price.




I plan to use hex stock and I have a box tool to turn the diameter and a die head to make the threads. The question is, what grade steel would be best for strength and ease of cutting? I do mostly aluminum so not much experience with steel.

Thanks in advance!
 

GoceKU

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#2
What grade of steel in hex is available at a affordable price is the question, having only small hex head may be more economical just to machine a hex on a round piece of bar, that way you can use cheaper, better quality material, also to consider is what type of finish are you using on the finished item, i've used 17mm C45 hex on a similar project and had the finished items hardened, which left a black finish and i counted them in cosmoline, do your calculations first because is hard to be cheaper then cnc manufacturing.
 

Bob Korves

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#4
A gear puller bolt will need to be hardened to take heavy loads and to have a good lifespan. 1144 does not harden well. I would tend to forget about using hex stock and machine the head to hex. Actually, I would first look for something made in quantity by someone else...
 

MrWhoopee

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#5
Were it me, I'd make them from ETD-150 and mill the hex. Similar to pre-hardened 4140 with better machinability. Alternatively, make them from a Grade 8 bolt.

If buying the bolt would cost more than making them, something is upside down.
 

Glenn Goodlett

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#6
I like 41L40 but I'm not sure it would be appropriate for a gear puller screw. But, it machines well.
 

tomw

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#7
Might I suggest doing your first bolts for another project, one less likely to injure your buyers if it all goes sideways. I use gear pullers quite often, and you can really put some stress into those bolts. If it broke, blood could easily be spilled.

Also, small batch hardening and tempering (required for this part) is not cheap, unless you have your own oven and know what you are doing.

Sorry if I sound like Ms. Debby Downer.
 

benmychree

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#9
A gear puller bolt will need to be hardened to take heavy loads and to have a good lifespan. 1144 does not harden well. I would tend to forget about using hex stock and machine the head to hex. Actually, I would first look for something made in quantity by someone else...
Also Stressproof can fail in torsion. I'd likely use 4140 HT
 

Asm109

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#10
What kind of hourly rate do you want to make with this product? If I make a bolt from hex, I would be making about $1/hour. I can buy one for $.75.
 

benmychree

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#11
One must realize that there are bolts and then there are bolts, varying widely as to tensile strength, and finding a high tensile bolt with threads all the way up, is a remote possibility, and also, a puller should have a much thicker hex head on it than a normal bolt so that a wrench will stay put on it while operating the puller, I do agree that it should be turned from round and the hex milled on, if the milling is done with straddle cutters and can be indexed quickly, it is not at all time consuming. I also concur with an earlier comment, that ETD 150 is a good choice for the part; it has a higher tensile strength (150.000 psi) than 4140 HT, at about 125,000 psi. On a turret lathe, jobs like this one can be done quickly, and CNC may not be justified in terms of setup versus numbers of parts to be run.
 

ecdez

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#12
Thanks to everyone for they're recommendations and input. Benmychree hit it right on the head though. Considering his comments as well as the others I may have to go a different route. I didn't consider the hardness aspect and stress that would be involved in a puller. I was still trying to figure it out mechanically and hadn't gotten to the details yet.

The bolt in the picture in my first post was from a site that sold them and it's $15.66. In contrast, I made some similar ones from aluminum hex (NOT for a gear puller) and after setting up the turret lathe I could crank one out in about 90 seconds. The lathe setup took about an hour though; figuring I'd make at least 20 that's only 3 minutes of setup per part plus 1 1/2 minutes to produce so 4.5 minutes each plus material. I've found the turret lathe to be very competitive against the CNC for short production runs. Especially since the turret lathe has me turning the handles and the CNC is in someone elses shop with their overhead and profit on top of each piece.

All that said though, I have to consider the safety aspect before I proceed. No profit, small or large, is worth someone getting hurt.
 

P. Waller

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#13
[QUOTE="ecdez, post: 590286, member: 17495")
All that said though, I have to consider the safety aspect before I proceed. No profit, small or large, is worth someone getting hurt.[/QUOTE]
What exactly is the "safety aspect"?
 

benmychree

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#14
I think you can still do better with your turret lathe than the price posted, you, (of course) need to use speeds and feeds appropriate for the material, especially for the die head threading. In my shop, I had no CNC, but turret lathes, and used them to advantage on short run jobs; for me, they were money makers.
 

benmychree

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#16
The definitive threading operation for this job is to roll the thread. Rolling the thread makes it harder and smoother which is highly desirable in a puller application…Dave.
That is true, and would be a good idea if one owns a thread rolling head or machine, but not a common item in the average shop.
 

ecdez

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#17
I think you can still do better with your turret lathe than the price posted, you, (of course) need to use speeds and feeds appropriate for the material, especially for the die head threading. In my shop, I had no CNC, but turret lathes, and used them to advantage on short run jobs; for me, they were money makers.
I love mine. Once it's setup the parts just crank on out.



The definitive threading operation for this job is to roll the thread. Rolling the thread makes it harder and smoother which is highly desirable in a puller application…Dave.
Now that would be a nice addition to my shop! What you say is likely true. It seems to make sense anyway.
 

P. Waller

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#19
I'm just picturing someones hand being close to it when the threads tear out. Maybe it'll never happen but I need to do my best to make it unlikely
I see, this is the type of part best made elsewhere for much less, it is likely that you could have 20,000 produced for less then $2.00 dollars each shipped to the US, unless it is a high end product with a brand name the consumer will always buy the lowest priced product given the choice.
 

kd4gij

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#20
What size puller are you making and How much force are you looking to achieve?
 

Bob Korves

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#21
The definitive threading operation for this job is to roll the thread. Rolling the thread makes it harder and smoother which is highly desirable in a puller application…Dave.
Agreed, Dave, and less stress risers, too.
 

whitmore

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#22
I have a small production run of specialized gear pullers I'd like to make and one of the parts

I plan to use hex stock and I have a box tool to turn the diameter and a die head to make the threads!
It could be most economical to fabricate it by starting with allthread (rolling is a very inexpensive way to make strong,
good quality threads) and pressing/brazing/epoxying a square or hex head. Hex is good to drive with a socket
wrench, square is good with an open-end wrench.
 
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