Tips on tramming the nod of benchtop mill PM25MV

[Wonderclam]

Can you guys help me find the bolts I need? I'm looking through Grainger and McMaster and I'm having problems navigating and finding the correct ones.

Also, was wondering how much torque is too much. I have one of those extendable 3/8" ratchets and that's what I used to tighten it down.

I was also thinking of maybe repairing the damaged threads on the bolt by TIG welding using stainless filler rod, then turning it down to size, and re-thread with a die

 

[matthewsx]

Precision Matthews should be able to give you the size bolts you need, you'll probably have to contact them for that spring anyway. And, the reason I suggested Fastenal or McMaster is that they actually have knowledgeable folks there who can help you navigate their catalogs. I know they are daunting, especially when you're searching online but as soon as you get the size and length and thread pitch you can give them a call and they will hook you up.

As for torque that's another question for the folks at PM. Buy a decent quality torque wrench, or get one from Harbor Freight if you're on a budget, it will be money well spent.

Welding a bolt with any kind of filler is unlikely to provide satisfactory results. If the fastener is hardened in any way you'll anneal it (make it softer), the materials may not be compatible with each other, and cutting new threads is going to be a job for a lathe or thread forming die, both of which cost more than just replacing the fastener not to mention the time you will waste doing it.

Stainless is probably not the material for this job, it has high strength but is usually more brittle which may not be desirable in this application. Usually stainless fasteners are needed only where rust or corrosion are a problem like outdoors or on a boat.

Read Carroll Smiths books if you can, he writes in a very easy to understand way and the knowledge he shares is useful way beyond race cars. Particularly "Engineer to Win" has tons of information on materials and how to build structures that will hold up under high loads.


Cheers,

John

 

[Wonderclam]

I might forego replacing the T bolts altogether. The threads don't look so bad, it's more one of the nuts that is chewed up

Another option I just thought of is to turn some high grade bolts down to size on the lathe and mill the rest for the T slot head.

I got some large grade 8 bolts that might work....

Maybe even make some nuts out of these large bolts. I'm thinking a "longer" nut would be harder to strip since there's more threads to bear the burden of tightening.

 

[RJSakowski]

I might forego replacing the T bolts altogether. The threads don't look so bad, it's more one of the nuts that is chewed up

Another option I just thought of is to turn some high grade bolts down to size on the lathe and mill the rest for the T slot head.

I got some large grade 8 bolts that might work....

Maybe even make some nuts out of these large bolts. I'm thinking a "longer" nut would be harder to strip since there's more threads to bear the burden of tightening.

For high strength nuts. Grade 12 is strongest.

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

 

[RobertB]

8.8 is a high strength metric fastener spec.

8.8 is approximately the same strength as an sae grade 5, a 10.9 is about the same as a grade 8.

It will vary by application, but a 10mm 8.8 should be torqued to about 55nm/40 ft-lbs.

 

[matthewsx]

8.8 is approximately the same strength as an sae grade 5, a 10.9 is about the same as a grade 8.

It will vary by application, but a 10mm 8.8 should be torqued to about 55nm/40 ft-lbs.

8.8 is 800 MPa minimum tensile strength which converts to 116030.190405776 psi, grade 5 is 120,000 psi so you are correct they have roughly equivalent specs which are fairly high strength. Provided the fastener in question comes from a reputable supplier it is most likely sufficient for the application and far better than the unmarked fasteners I've seen installed on many Chinese tools. I've trusted 8.8 fasteners to hold together the racing karts I built for my customers as well as in many other applications.

However the key thing I was trying to get across is this.

Unfortunately, fasteners like many other things made in China aren't always what they claim, sometimes they just copy the form without duplicating the spec.

and

Since you're in Santa Clara (where I was born BTW) you can go into Fastenal, Grainger, or possibly another supplier that caters to industry and purchase the right fasteners for the job. You will pay a little more than ordering online or at the local big box store but you will be able to ask questions and get the parts you need to make sure things stay where you put them.

I'm fairly sure that PM can give the OP information on the fastener in question, and the torque spec. The challenge is that unscrupulous parts suppliers could possibly introduce counterfeit fasteners into the supply chain. I'm not trying to say this is the case here, just that when replacing fasteners it's worthwhile to go with known suppliers rather than whatever is cheapest on Amazon.

Also it's worth noting that using a higher tensile strength fastener that what is specified can cause it's own problems. There are many applications where it's preferable to have the fastener deform rather than snap off. Choosing fasteners, like selecting any material is a trade-off between hardness, toughness and strength.

Here's an info-graphic about it.




Getting these trade-offs correct is where engineering comes into play. I'm not an engineer but I was raised by one and I'll always remember as a kid crossing a bridge with my dad while cars were driving across it. I was concerned by the fact the bridge was moving under my feet and told him so. He said "son, if it doesn't flex it will break".
I miss that man....

Cheers,

John

 

[RobertB]

Provided the fastener in question comes from a reputable supplier it is most likely sufficient for the application and far better than the unmarked fasteners I've seen installed on many Chinese tools.

You mean like those unmarked fasteners that come with wrenches that are 3" long and stamped out sheet metal to assemble them with because any decent wrench will twist the heads off?

 

[matthewsx]

You mean like those unmarked fasteners that come with wrenches that are 3" long and stamped out sheet metal to assemble them with because any decent wrench will twist the heads off?

Yep, those ones for sure

 

[Wonderclam]

Turns out the bolts weren't damaged. The nuts were the ones that stripped. Bought 3 new stainless nuts and tightened the mill head as much as I can, thinking it would strip the bolts. I gave it all my strength, but could not strip them. I guess they're fine now.

 

[matthewsx]

Turns out the bolts weren't damaged. The nuts were the ones that stripped. Bought 3 new stainless nuts and tightened the mill head as much as I can, thinking it would strip the bolts. I gave it all my strength, but could not strip them. I guess they're fine now.

So, you used the Armstrong torque wrench?