Fasteners - Thread Inspection Questions

N

NCYankee

#11
Randy & Umang,

Again, thank you both for your input.

The problem isn't so much with the tranny when it's being used, but just when being put together. The wall thickness wasn't as much as I thought. It appears to be as little as 1/8" or so at it's thinnest point (toward the outside of the bolt ear). The problem is happening when the customer is torquing the stud down. Not only is the bolt hole stripping out, but it now appears the ear is cracking. We are looking at adding some material (actually, not removing as much material) to strengthen the ear.

As far as a cost study....can't do right now. Need a method right now, and I'm going to have to buy something by tomorrow at the latest. It's just a matter of what I buy.

I repeat my thanks for your assistance. :thanx::thanx:
 
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N

NCYankee

#12
Mr. Rosen,

Thanks, but I know inspecting won't fix any problems. As I stated previously, we're a small company. We don't have a lot of money in the budget, nor do we have anything to measure or check this newly designed part. That's why I was looking for the cheapest method of inspecting the part. :thanks:
 
U

Umang Vidyarthi

#13
Randy & Umang,

Again, thank you both for your input.

The problem isn't so much with the tranny when it's being used, but just when being put together. The wall thickness wasn't as much as I thought. It appears to be as little as 1/8" or so at it's thinnest point (toward the outside of the bolt ear). The problem is happening when the customer is torquing the stud down. Not only is the bolt hole stripping out, but it now appears the ear is cracking. We are looking at adding some material (actually, not removing as much material) to strengthen the ear.

As far as a cost study....can't do right now. Need a method right now, and I'm going to have to buy something by tomorrow at the latest. It's just a matter of what I buy.

I repeat my thanks for your assistance. :thanx::thanx:
1.Since there is'nt sufficient wall thickness to insert a steel sleeve,the last option available is to insert the whole receptacle (the part/ear for homing the stud)-made of steel harder than the stud-to the main case.

2.I have conducted the cost study,which comes out in favour of the TPG & Ring gage.

3.As a last resort you may opt for Thread Micrometer,since the Three wire method is cumbersome,needing an expert to handle.

Have your pick,try,and share the results on the cove.Good luck.

/Umang :bigwave:
 
N

NCYankee

#14
To all:

I just found out that we were thinking backwards on how UNJF and UNF fasteners and holes fit together.

Incorrect: UNJF fastener into UNF threaded hole.
UNJF external threads must go into UNJF internal threads.

Correct: UNF fasteners may go into UNJF threaded holes.

However, from what I've seen on the web, and heard around here talking with the Design Eng., it's almost impossible to find a UNJF tap for threaded bolt holes. The usual recommendation is that a UNF tap is fine, but to check with a UNJF threaded GO plug gage.

Thoughts?
 

Randy

Super Moderator
#15
Yep...go to aircraft standard on all your fasteners. They work on everything from a Cessna 150 to the Space Shuttle in most applications.

Additionally check with someone like Gibbs. Hendrick or Petty in NASCAR.

You may have to engineer some type of collar arrangement or an entire steel plate that is bolted flush with the mating surfaces that contains that will allow both parts to be mated. I 've seen when a magnesium case is machined down and steel mounting flanges are substituted for the removed material. Your dealing with high torque and under many normal applications in a racing environment magnesium alloy won't take the strain,
 

Wayne

Gage Crib Worldwide
#16
Hi everybody. I've got an issue and I'm not sure how to deal with it. Let me explain. I'm working for a small company that makes transmissions and rear ends for the oval track racing circuits. Money to buy things like ASME specifications and such is limited or isn't available. This is why I'm asking for so much assistance.
For your application you can use the Free 10-Day Trial of ThreadTech Software. Ten days is long enough for you to do the thread engineering you need to get the answers about thread specifications your require. The software is for sale for $410 but unless you have frequent thread questions, you should be able to get buy with the free trial period.
 

Wayne

Gage Crib Worldwide
#17
Here's my first question: Will a 5/16-24 UNJF-3A thread on the stud engage with the 5/16-24 UNF-2B threaded bolt hole on the main case? If so, great. If not, will they need to redesign the callout on the main case to 5/16-24 UNJF-3B?
Let me say that if you should read: UNF vs. UNJF. Now to specifically answer your question. The two points of interest in the mating of these specific threads are the pitch and minor diameters.

First we will discuss the pitch diameters. The pitch diameters do not change between UNF and UNJF. The respective pitch diameters are:
3A = 0.2854"/0.2827"
2B = 0.2854"/0.2890"
3B = 0.2854"/0.2827"

Note that the maximum material condition in all three situations is the identical same value of 0.2854". This is by designed per ANSI B1.1. The possibility of interference between male and female threads is unlikely for many reasons beyond the scope of this discussion. Just let it be said that this condition is acceptable and does not cause interference. What is important here is that the 3A will screw into either the 2B or 3B.

Second we will discuss the minor diameters. The minor diameters do change from UNF to UNJF. Of course, by design there will be no problem assembling UNJF-3A to UNJF-2B or UNJF-3B. The respective minor diameters are:
3A UNJF = 0.2644"/0.2591"
2B UNF = 0.2670"/0.2770"
2B UNJF = 0.2719"/0.2799"
3B UNF = 0.2670"/0.2754"
3B UNJF = 0.2719"/0.2799"

When you review the relationship between the UNJF-3A and the UNF-2B and UNF-3B minor diameter it might appear that there is not interference, but the UNJF-3A root has a 0.0075"/0.0063" root radius. This root radius will intersect the minor diameter of the UNF internal threads in some conditions. Comparing the minor diameters between the UNF and UNJF threads there still be found an overlap zone where UNF will make with the UNJF external thread without inference. In the remainder of the minor diameter zone, there may be or may not be interference depending on the physical size of the external thread. Because of the possibility of minor diameter interference between the male and female thread it is generally not recommended to assemble external UNJF to internal UNF threads. BTW: The opposite assembly will mate with no problems.

In your specific situation, my personal opinion is that you will be able to assemble external UNJF to internal UNF threads because of the softness of your internal thread material. It will deform itself onto the UNJF external thread with minimal to the thread and no structural weakening of the internal thread.
 

Wayne

Gage Crib Worldwide
#18
Second question: Will the nuts that are put onto the stud (both sides) need to be 5/16-24 UNJF-3B?
Based on my previous post: Yes.
Third question: Since we are going to have to buy some type of gaging to measure these studs &/or tapped holes, what would be the most inexpensive, but good way to inspect these? Threaded Ring Gage? Thread Micrometer? Three-wire? If three-wire, what size wires would I need?
Thread gages are the most cost effective method of measuring threads considering the cost of the gages and the time spent measuring the threads.
Fourth question: If the threaded holes and nuts need to be changed to the 5/16-24 UNJF-3B callout, what's the most inexpensive, but good way to inspect those?
Again, thread gages are the most cost effective method of measuring threads considering the cost of the gages and the time spent measuring the threads.
 
Last edited:

Wayne

Gage Crib Worldwide
#19
However, from what I've seen on the web, and heard around here talking with the Design Eng., it's almost impossible to find a UNJF tap for threaded bolt holes. The usual recommendation is that a UNF tap is fine, but to check with a UNJF threaded GO plug gage.
The only difference between UNF and UNJF internal threads is the minor diameter. The tap does not address the minor diameter and thus there is no difference between a tap to cut UNF and a tap to cut UNJF threads. If some one is charging you extra for a UNJF tap, they are taking advantage of your naivity.
 

Wayne

Gage Crib Worldwide
#20
Additionally in a magnesium case you need steel inserts for the actual fastener itself. The inserts may even need to be pinned.
I assume that you have heard of screw thread inserts, trade name Helicoil. This video (lower right corner of this webpage) says it much better than I can. It will explain why the screw thread insert will be your best design option after you add some material to your flange.
 
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