Engineering Question - Bolt Grade and Material

[Pooh_Bear]

I am building a scrape blade.
I need a bolt for the blade to pivot on to set the angle.
The bolt I need is 1 inch diameter and 8 inches long.
What material and grade of bolt should I use.

See attached picture to see which bolt.

Thanks.

Pooh Bear

 

[Defective]

I wouldn't use a bolt. Bolts are not designed for shear loads and if you torque the bolt properly to put it in compression instead of shear you'll curse every time you need to change the angle.

I'd use a hardened pin with hardened washers top, center and bottom.

 

[Pooh_Bear]

Wouldn't a grade 8 bolt be about the same as a hardened pin?

I won't be changing the angle very often.
I don't mind messing with bolts to do this.

Pooh Bear

 

[Lindblom Lawn Care]

A hardened pin I think is a bit more stout. I don't think it is quite grade 40, some might be.

Might look for something like a spindle, can handle the shear load and use a castle nut. That would allow the required ability to angle the blade, provide shear protection.

Check out boltcouncil.org. or a hardware guru. A 1" grade 8 might be able to withstand a shear load required for the blade. Might have ask some smarter than me.

 

[gizmo]

My blade is similar to yours and uses a 1" grade 8 bolt, washer top and bottom, and a lock nut snugged up just enough to take up the slop. Bear in mind that my blade is about 30 years old and has had a lot of "work" done to it. However, the bolt has worked well so far. The blade is 72" wide and I have loaded it to the limits of 4WD traction without any problems.

 

[MadReferee]

I used a single 1" grade 8 bolt for my pivot and 2 7/8" pins to lock it into place. After 3 years and plenty of abuse I have had no problems.

 

[scott_vt]

Mornin Pooh Bear,
You might consider a shoulder bolt rather than a standard bolt !

 

[Renze]

Bolts can take all kinds of loads: compression, pulling, shear, bending.
Lower grade bolts can take more deformation before they crack.

When you guys mention grade 8 bolts, is it the same as 8.8 quality bolts they sell in Europe ? 8.8 are able to take 800 N/mm2 (which is 80 kg per square mm of diameter surface)

All 8.8 bolts are electrolyticaly zinc coated.
You cannot buy thermically zinc coated 8.8 bolts because the heat of the zinc bath changes the characteristics of the metal back to the level of the original material before the strength treatment. Same is with welding, if you heat up the material of an 8.8 bolt, reckon its equal to 4.6 bolts, which handle about 600 N/mm2

For making anchors to be poured into the concrete to mount metal structures on, usually 4.6 is taken, because 8.8 will crack in 80% of the cases when you bend a threaded rod into an L shaped concrete anchor. 8.8 is stronger but stiffer and will crack sooner at a lower level of deformation.


OOh, and for the practical side of the story: it might be handy to weld a solid rod on either the bolt or the nut, so you can adjust the angle without having a wrench with you on the job.

Most scraper blades i've seen have a toothed ring that holds the blade at angle, so you can adjust it in steps of 15 degrees or something. You can make your own by welding some L shaped bars on the scraper top plate, and two strips of metal (wedge shaped like a portion of apple pie) on the A frame, to lock up inbetweent the L bars.

 

[Pooh_Bear]

Well, I guess a grade 8 bolt it is then.
I won't be doing much adjusting "in the field".
I'll never be more than 600 feet from the shed at any time.
If I need to adjust it I'll just go get a wrench.

This thing won't see a lot of use or abuse.
The hitch structure is built like a tank.
Only weak points are that pivot bolt, and the 4 bolts that
will hold the blade to the pivoting mounting plate.

My tractor is a 1949 8N.
I don't think there is enough HP there to do any damage to the blade.
Mostly gonna spread loose dirt, mulch, and gravel.

My house and property.
http://web.infoave.net/~poohbear2767/panorama.htm

Thanks.

Pooh Bear

 

[mopacman]

Try to put the solid part of the bolt in the shear area instead of the thread part. This makes the shear strenth alot higher and it won't ware out in the pivet as fast. Don't use all thread which is soft.