Lots of different aluminums out there. Some cut and thread fine and some are soft and gum up the cutters. Some are very strong and do not like to bend and some bend easy but are weak. Normally the closer to pure aluminum, the softer it is. I like to use 6061T6, It machines nice and has the strength, but it does not like to bend. The softer more pure alloys will have a slivery look while the stronger stuff tends to has a more light grey color. Use cutting fluid made for alumin.

?Jeff

On Wednesday, August 16, 2023 at 01:10:12 PM EDT, Peter Brooks <peter@...> wrote:

Thanks everyone for the very detailed replies and discussion - fascinating.

I found out myself yesterday why bolts aren’t made from aluminium. I might as well have been trying to put a thread on a bar of chocolate. It was not a success. Oh well, you live and learn…

There are copies of Machinery's Handbook , various ages, from about ?5 upwerds. Also shorter versions, how to use it books etc.

I (not an engineer) was told a long time ago that Whitworth (who first analysed screw threads mathematically) came up with some generalities which I remember as follows:

Tap a hole in something soft {eg cheese) and screw the bolt in by 6 turns. Now force the bolt out. In the bolt's thread there should be a triangular cheese spiral.
Apparently the area of sheared cheese should be about the same as the cross-sectional area of the bolt.
Conclusions:
If you screw a bolt into a tapped hole of the same metal deeper than about 6 turns then overload it the bolt will break (less metal than the total metal in the threads.
If you screw a bolt into a tapped hole in weaker metal by fewer than about 6 turns then overload it then the hole will be stripped but can then be helicoiled.
If you screw a bolt into a tapped hole in stronger metal by fewer than about 6 turns then overload it then the bolt will be stripped leaving swarf in the hole that might be a (obscenity) to remove.

Is this generally correct?

Ian

You don't need to do #2 if you are using the correct tap with a right hand spiral flute because it will eject the chips as they are made:

2. For blind holes, if possible, you want an extra 1 diameter of tap drill depth to have room for chips to fall during tapping.?

Here is a video of the spiral tap in action:?

You will get easier results with less effort if you pick the right tool for the job. In the case of taps, the price is not really an obstacle, as they are quite affordable.?

---

From: [email protected] <[email protected]> on behalf of Tool247 <Sjkochan@...>
Sent: Tuesday, August 15, 2023 6:39 AM
To: [email protected] <[email protected]>; d.seiter@... <d.seiter@...>
Subject: Re: [Unimat] Bolt queries

?

Hi Peter,

Some good “rules of thumb” for designing with bolts.? These were bestowed on me over 35 years of mechanical design and product development from gifted and generous mentors.?

1. For steel bolts into mild or stainless steel, 1.5 diameters of thread will engage the full strength of the bolt threads. For example 1/4-20 ideally should have 3/8 min full thread.?

2. For blind holes, if possible you want an extra 1 diameter of tap drill depth to have room for chips to fall during tapping.?

3. For good steel you can go as little as 1 diameter for the thread strength but 1.5 allows for drilling pilot oversized. Research into thread strength has indicated that as little as 2-4 threads truly carry the full load of a bolt, but redundancy of 4-5 threads is a safe absolute minimum.? It takes into account thread yield and settling in of both bolt and nut threads.?

4. Aluminum bolts should not be considered structural bolts unless highly engineered , and anodized or hard coat anodized. Over time aluminum bolts oxidize and lose ductility. Aluminum bolts used anywhere need grease like lube. And yes over time an aluminum bolt and nut or thread joint will oxidize.?

5. For structural bolts into aluminum it takes 3 diameters of full threads to engage the full strength of a steel or stainless steel bolt. I have used both stainless and alloy steel in aluminum successfully. Best practice is to use grease on both. If you have ever seen aluminum car rims on a car after a few winters with road salt, the mating surfaces are always corroded and pitted and usually seized together from galvanic affect. Grease does help.?

Btw 18-8 or 304 stainless bolts are approx 40ksi yield and 80ksi ultimate strength. Socket head screws from unbrako or cam car or metric with stamped heads are usually approx 2x the strength of stainless.?

6. The failure in a bolted joint is always the bolt if it is pure tension. This is due to the small cross section of stress area. For this reason for steel in steel a fine threaded screw is always stronger than a course thread but assumes perfectly formed tapped hole. If the pilot drill drills over size you can quickly go from 75% engagement to 60 or 50 with just a couple number drill sizes. That is why most mechanical designers avoid fine threads in structural applications.? Also this allows you to pair high strength bolts with medium strength nuts because the nuts have properly formed threads.?

7. Important rule of thumb….if the screw looks too small, bump it up a size or 2.? Combined stresses in bolted joints can be considerable.?

8.? Minimum distance for a tapped hole or tight clearance hole for a bolt from the edge of a plate should be about 1 diameter. That is from center line of hole to edge. This engages full bolt strength and full clamping assuming the plate is approximately 1 diameter thick minimum. This usually eliminates plate hole tear out.?

9. It is easy to calculate tensile force or shear force in a joint and is tempting to use 1 bolt to do the job. Don’t fall for this temptation in critical joints. Minimum of 2 bolts is better and 3 bolts is best as a minimum. This helps mitigate unplanned bending. There is an old saying that any bracket is a step. Don’t want anyone getting hurt. Assume human body weight.?

10. Factors of safety. Any non-critical joint 1.5x.? Critical joints with shock loading 5x-8x factor of safety.? Overhead lifting 10x-12x FOS.?

Disclaimer: ?All above info is for reference only. Any critical fastener joint requires formal engineering. Just being conservative. ;)

Enjoy.?

On Mon, Aug 14, 2023 at 12:45 PM Dave Seiter <d.seiter@...> wrote:

Machinery's Handbook is a great source, but if you're going to get a used copy, newer editions will be better than older editions for metric info.? I have 4 or 5 editions, the oldest being from the 50's.? I've found that while most of the general info remains fairly constant throughout the years, more specialized data may require a little digging through multiple editions. I specifically remember needing a table of collet dimensions, which I'd seen before, and the book I grabbed did not have ANY data on collets.? (I think it was from the 90's). Newer and older editions did have the data.? If you're looking for information on old tech, like flat belt drive, really old editions would obviously be needed.?

-Dave

On Monday, August 14, 2023 at 03:52:22 AM PDT, Carl <carl.blum@...> wrote:

Hello Peter:

?

Machinery's Handbook also has Metric information, it will tell you USA measurements are based on the meter. Check Ebay or bookstores for a copy, even the early editions are useful. New they are about $100, but I've found used for $10. The book is a great read, everything from flooring to finance. It's size has stayed the same to fit in that small drawer in Girshner tool boxes.?

?

?

?

?

?

In tool making we always used stronger bolts. Aluminum would only be used for appearance or weight. Stainless bolts in stainless are prone to galling, this week I had a 1/4" screw gall in a stainless flange and I had to saw it free. I'm on the road with no grease so I used butter and finished the job.?

On 08/14/2023 2:45 AM EDT Peter Brooks <peter@...> wrote:

?

?

Thanks Bill. Is that an American book?? We are (for our sins) now?generally metric over here in the UK, I wonder if there is an equivalent?

Machinery's Handbook is a great source, but if you're going to get a used copy, newer editions will be better than older editions for metric info.? I have 4 or 5 editions, the oldest being from the 50's.? I've found that while most of the general info remains fairly constant throughout the years, more specialized data may require a little digging through multiple editions. I specifically remember needing a table of collet dimensions, which I'd seen before, and the book I grabbed did not have ANY data on collets.? (I think it was from the 90's). Newer and older editions did have the data.? If you're looking for information on old tech, like flat belt drive, really old editions would obviously be needed.?

-Dave

On Monday, August 14, 2023 at 03:52:22 AM PDT, Carl <carl.blum@...> wrote:

Hello Peter:

?

Machinery's Handbook also has Metric information, it will tell you USA measurements are based on the meter. Check Ebay or bookstores for a copy, even the early editions are useful. New they are about $100, but I've found used for $10. The book is a great read, everything from flooring to finance. It's size has stayed the same to fit in that small drawer in Girshner tool boxes.?

?

?

?

?

?

In tool making we always used stronger bolts. Aluminum would only be used for appearance or weight. Stainless bolts in stainless are prone to galling, this week I had a 1/4" screw gall in a stainless flange and I had to saw it free. I'm on the road with no grease so I used butter and finished the job.?

On 08/14/2023 2:45 AM EDT Peter Brooks <peter@...> wrote:

?

?

Thanks Bill. Is that an American book?? We are (for our sins) now?generally metric over here in the UK, I wonder if there is an equivalent?