# Tag Info

10

As Dave Tweed points out, the ratio of torque to tension is lower the lower the lead angle is. Since the important measure of bolt tightness is generally the tension in the bolt, we want to achieve that minimum pretension with the least effort possible. Assuming we have to maintain a certain shear area of the thread (so the the threads are stronger than the ...

10

I'm not a machinist, but I've tapped a few holes in my time. In my experience a tapered tap will handle this problem as the taper will reach down to the good threads and self align. Use some oil with the tap. I looked at your link and that tap doesn't have much taper so perhaps a more tapered tap might help if you have problems. There are any number of ...

9

I asked a friend who is a highly competent EE by day - but who restores super sized steam engines by night and collects olde heavy metal engines etc and has much experience with old large corroded items. His comments: It really depends on the specific situation. For mild steel bolts in good condition which have not been too excessively deformed, and where ...

9

For any given size of fastener and given thread pitch, a single-start thread gives you the greatest mechanical advantage in terms of the torque required to achieve a given tension. Aside from acme threads that are often used on leadscrews for mechanical motion (e.g., CNC machinery), the only other place I have seen multiple-start screws is on self-tapping ...

9

The product that you're describing (an 'expanding tap') doesn't exist, unfortunately. I had a similar problem a few years back, and actually built my own out of a Sleeve anchor, like the one pictured below. As you tighten the nut, it pulls a tapered cone inwards, pushing the sleeve apart. I loosened the nut until the sides were parallel, shaved down the ...

7

First, I want to say that I'm suspect of that material actually being ASTM A311 (though I don't have a copy of that standard available to verify.) Looking on Matweb, this material is the closest I found in the 1050 steels. This search turns up quite a few results, but from what I can tell of A311, it's for cold-drawn and stress relieved bars, but doesn't ...

7

Threads To have the thread automatically reengage some thought will have to go to the exact type of thread used. A coarse thread and maybe a slight taper will help the threads to properly engage while minimizing the chance of cross-threading or binding. Mechanism You said that eventually the inner piece will disengage from the outer piece. This doesn't ...

6

28 is a standard Threads Per Inch dimension for 1/4 and 1/2 inch screws. $\frac{25.4 \,\text{[mm/Inch]}}{28\, \text{[Threads/Inch]}} = 0.9 \,\text{[mm metric pitch]}$ The 27 seems strange to me. But I usually use metric bolts.

5

You could drill out the hole to remove the munged threads down to the remaining good threads. This should make it easier for the tap to get into the thread grove correctly. Another thought would be to grind out the damaged threads if you could get a small cylindrical grinder. (Thinking Dremel tool here)

5

The pink Arrow hole should be left smooth. If both holes have threads when you turn the screw into the pink hole as soon as it passes the gap and reaches the yellow hole, it will keep the gap space constant. Turning the screw more will just drive it into both holes while keeping the gap at the same space till the head of the screw jams onto the lower ...

4

To make this work, one side will need the "normal" righthand thread and the other a lefthand thread or a rotating connection , but threads on both ends of the nut will not change the tension.

4

A relatively inexpensive and quite useful device would be a "pocket optical comparator". They come with Several etched glass plates with features of size that you optically/visually compare to your part. I'm happy to explain more if need be. Furthermore, you can also use a two-part rapid set silicone mold material to take molded impressions of your ...

4

Metric bolts use thread pitch in millimeters. Your M3 screw likely uses the standard pitch of 0.5 millimeters. One complete rotation of the screw will advance the screw into the work piece by that amount. According to the Bolt Depot chart, there is only one standard pitch for M3 screws, although other sizes will have standard, fine, super fine pitches ...

4

The threads made by the tapper used for helicoil is not going to work with the standard size bolts. The taps used are specific STI (Screw Thread Insert) tools. But of course, if you decide the old thread is not too damaged you can use a standard tap and try to fix it.

3

In 1841 Sir Joseph Whitworth produced a paper on a universal system of screw threads. He then collected a variety of screws and proposed a universal thread using their average pitch and depth. The result was the 'Whitworth thread' with the depth and pitch of constant proportion, giving the 'V' thread a mean angle of 55 degrees and the number of threads per ...

3

Firstly, in reference to nomenclature: in ISO (metric) standards the pitch of a leadscrew is given in units of distance/revolution. However, Unified (inch series) standards, pitch is given in TPI (threads per inch). As you mentioned in your question, lead is related to pitch by $p = L/N$ where $p$ is the pitch, $L$ is the lead and $N$ is the number of starts....

3

I think the pitch is implied by the major and pitch diameter. The tolerance of these $D_{maj}$ and $D_{pitch}$ are given in ISO 965-2 I'll attempt juggling with the math in the ISO metric screw wiki, (please correct if wrong): $(3/8)H=(D_{maj}-D_{pitch})\cdot(1/2)$ $H=P\cos(30^\circ)=P\sqrt{3}/2$ \$P = \underbrace{(2/\sqrt{3})\cdot(8/3)\cdot(1/2)}_{1....

3

Well I would suggest that you don’t thread one of the items - just have a clearance hole then a locking nut. Then, to get a precise position have a hole with a locating pin - this will ensure the positioning.

3

You need clearance at the bottom of the threaded hole or shorten the depth of the thread. This is to allow for the machining process and clearance for the cutting tool. Otherwise your thread will not be a long as you specified(because the machinist needed clearance, or the machinist will break a tool or drag the tool at the bottom of the hole if they are not ...

3

The most common way to fix mangled threads, if they're really beyond fixing and if there's enough meat to open the hole a bit larger, is to use something like a heli-coil (aka : threaded insert). For a given thread, a helicoil will have a special oversized drill and tap which you use to clear out the mangled threads to a larger diameter and tap. After ...

3

A metric thread table is what you want. Table 1. Source: Anzor. So is there a standard rule of thumb, or equation about the distance the end of a screw will travel per rotation? It's not a rule of thumb - it's defined by the pitch. Conversely, how many turns it will take to travel a specific distance? Turns required = distance / pitch. Say I have ...

3

Why does the helicoil need to be inserted if you have already tapped the new threads into a hole? Can't you just put a bolt in once you've tapped new threads? Consider the case of an M5 x 0.8 tapped hole. The helicoil will need the same pitch (0.8 mm) with a larger diameter hole. Note that the M6 is a 1.0 mm pitch so even if the helicoil tap was the same ...

3

Short and simple, if you want to use the same size fastener again, you have to use a helicoil. By drilling out the old thread with the new pilot hole you have made it larger thus the fastener size will go up unless a helicoil is used to take up that change in diameter. Further more, helicoils also prevent the threads from needing to be repaired in the future,...

3

Use a planetary gearset. Drive the center continuously at the speed you want to tap. Use a mutilated gear to drive the ring in the opposite direction intermittently and at a speed that will back the chuck up. The chuck runs with the pinion gears. There needs to be a dog clutch rigged to the mutilated gear to hold the ring gear fixed when not backing it up. ...

2

I'm sure there are specific strategies relating to pipe flanges, but for the broader issue of controlling that all of your bolts are tight enough, here is some background information. When tightening bolts in any clamping application, what's really important is the total clamping force. In any simple joint, and specifically when dealing with pipe flanges, ...

2

Although i know is's not the right answer, i would like to mention that using a micrometer to measure bolt length out of nut can be helpful, because that is proportional to torque, so for same installations one can use it to check if all bolts have the same load. another option when a torque meter is not helpful is to use smart bolts. they have internal ...

2

I am not aware of anyone that makes such a beast nor have I seen one in the wild. What I have seen is head collars. collars are a tapered washer normally made of nylon but also available in metal that are designed to accommodate mismatched head taper. As they have no threads they can be used with multiple screws. Somewhere I have a box of them for #8 screws. ...

2

If you have a vendor you work with, or even if you don't work with them but you're aware of their company, then I would ask them directly for the formulas/references you should use to spec the housing for their equipment. I know from working with sales application engineers that they are very eager to help you design your system if it means you're (telling ...

2

I always cheat the thread engagement percentage in tough materials. When allowable of course, going from say 75% to 65% will make it much easier to tap. So for a M12, chart says letter "Y" drill at .404" will give you 75% engagement. I'd try going up to letter "Z" drill at .413". ONLY if you can! Otherwise, it sounds like your problem is chip extraction, the ...

2

Usually threads are done by some standard. You can use calipers to measure and than find closest in standard, if your product is from eu, its easy you need eu standards like this ISO 68-1:1998 or maybe BS pipe So the answer would be to measure as accurate as possible but also use literature. Mechanical engineering handbooks like Kraut are great to have at ...

Only top voted, non community-wiki answers of a minimum length are eligible