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Set screws: cup to dog point

trlvn

Active Member
#1
I'm embarrassed to say this, but some itty bitty set screws are kicking my butt!

I want to replace the gib screws on my tiny Atlas 618 lathe. They use a slotted drive and I broke one the other day. I figured I'd replace the screws on the compound (4 X 8-32 by 1/2") and the cross slide (3 X 10-32 by 5/8"). These are "dog-point" screws where the dog engage in a little depression in the gib so it doesn't get left behind. I want to switch to hex drive screws. In the following picture, the original parts are above the ruler and the new cup point screws are below.

compound cross_slide gib screws.jpg

But BoltsPlus did not have any dog point screws in stock and I'd have to order a box of 100 of each size ($12 X 2). I thought I'd buy cup-point screws and then use the lathe to form the dog point. I tried to use my HSS parting tool to cut the dog point and promptly ruined the edge. I've never really used them, but I do have a few braised carbide bits that the previous owner sharpened. I selected the best looking one and got a little better cut but the tool pressure pushed the part back into the chuck. I had wrapped the screw in a piece cut from an aluminum can to try to protect the threads from the chuck jaws.

These screws must have been hardened and tempered, right? I don't think I want to anneal them, do the work and then re-harden/temper.

If I had a tool post grinder, I think that would be the easy solution. Alas. Perhaps I could freehand it with my Dremel? Not crazy about this because I'd have to be so close to the chuck.

I've wondered about chucking them in a drill and freehanding against the bench grinder or 1" belt sander?

Any suggestions before I try something that turns out badly? ;)

Craig
 

ducdon

Active Member
Premium Member
#4
Throw a socket head cap screw in your lathe and turn the point down to a Dog Point. It will work fine.
 

trlvn

Active Member
#5
Throw a socket head cap screw in your lathe and turn the point down to a Dog Point. It will work fine.
Are socket head cap screws not hardened? I can't find it right now but one of the web sites I visited showed that these dog point and half dog point set screws are Rockwell 43 (I think). Not crazy hard but hard enough.

Craig
 

Tom O

Active Member
#8
To my way of thinking it isn’t under any strain as it’s a locating fit so the gib doesn’t slide out while keeping minimal pressure for proper tramming.
 
#9
I did. They could supply the 8-32 X 1/2 but not the 10-32 X 5/8. Nothing bigger than 1/2" and I really need that extra eighth. McMaster-Carr won't ship from the USA. Fastenal wants $2 EACH...and I just don't like them that much.

Craig
Does McMaster-Carr have retail locations or are they internet only?
 

ducdon

Active Member
Premium Member
#10
Are socket head cap screws not hardened? I can't find it right now but one of the web sites I visited showed that these dog point and half dog point set screws are Rockwell 43 (I think). Not crazy hard but hard enough.

Craig
I just did a set like that for the fence stops on a woodworking jointer cause the dog point set screws were completely mangled. I had no problem turning them down. Only need to cut them enough to remove about a quarter inch of thread.
 

trlvn

Active Member
#12
I just did a set like that for the fence stops on a woodworking jointer cause the dog point set screws were completely mangled. I had no problem turning them down. Only need to cut them enough to remove about a quarter inch of thread.
I'm still in my rookie year so I get to ask dumb questions. :confused: Are most machine screws and bolts hardened? Makes sense to me--especially for the heads--to resist deformation.

Could I have some more details, please? Did you hold them by the head to do this? 3-jaw chuck? Carbide or HSS for the cutting? Anything other tips?

Thanks,

Craig
 

ducdon

Active Member
Premium Member
#14
I'm still in my rookie year so I get to ask dumb questions. :confused: Are most machine screws and bolts hardened? Makes sense to me--especially for the heads--to resist deformation.

Could I have some more details, please? Did you hold them by the head to do this? 3-jaw chuck? Carbide or HSS for the cutting? Anything other tips?

Thanks,

Craig
If I recall I ran them through a nut and held the nut in the 3 jaw chuck. SHCS are very tough (high tensile strength) but not really hard. Any cutter used at appropriate speed will work. Don't over think it. Worst you can do is dull a bit or garbage a screw.
 

PeterT

Ultra Member
Premium Member
#15
I haven't had too much difficulty turning down typical cap screws. I've had to use light cuts & cutting oil. The hardness might be more around the threads, at least it seems that way to me. Maybe they roll vs cut threads & there's some added work hardness?

The fussier issue is how to hold them properly. I have tapped some round stock & threaded the bolt in from behind. The head mates the end of the stock but it still is better to have a jam nut on the chuck side so it doesn't loosen under cutting. Problem with a set screw is it needs a nut on both sides so maybe not great for shorties. I have gripped threaded rod in a collet but I don't like doing it. If it spins its might be hard enough the scour the collet. I've used a couple winds of metal foil tape or brass shim & gripped with a 3-jaw (so as not to bugger the threads). It works but again light cuts.

Another option is if you can drill the end of the set screw & insert a dowel pin with permanent retaining lock. But I guess if you can drill the stuff you can probably turn it too.

I can visualize a makeshift jig that might work. Basically a stick of metal with a hole closely fitting the OD of set screw. Put the set screw in the hole, maybe a nut to act as a depth stop. Put a hex key in the end. Grip the block so its on your grinder table & hold with one hand & spin the set screw with the hex key in the other. If you can slowly regulate infeed with your hand you might get something reasonable. It wont be as nice or as accurate as turning I suspect.

McMaster wont sell to Canada unless you have a corporate / government / educational type account. Its been that way for years. With all the trade crap going on they might resume service when hell freezes over.
 

trlvn

Active Member
#17
Well, my offer still stands. If you cant make these let me know a part number and I’ll grab what you want from the USA for you

Erie PA and Buffalo NY are the two biggest cities I’ll be in today
Really appreciate the offer but surely I can get something to work.

If I really screw up, I'll buy the boxes of the proper fastener. There is a mailing list dedicated to Atlas lathes with a lot of 6 inch users. I'll offer up the excess screws to them.

Craig
 

trlvn

Active Member
#18
BTW, just to show how far down the rabbit hole I am...

I found some internet plans for a poor man's tool post grinder using the Dremel. I'm thinking about this to make the dog point on the gib screws...

I want better gib screws because my homemade milling attachment wasn't locking down well enough...

The milling attachment is to cut some slots for parts to mount the motor on an Atlas 10-F. I really only took the 10-F to help an older friend who needs to downsize his tool collection.

I can just picture that I'm soon going to be collecting iron ore to smelt some steel to make a part to ... ;)

This machining hobby is more recursive than any programming I've done!

Craig
My buddy does a little driveway blacksmithing. We did melt some steel once--by accident! Amazing what a blower on a coal fire will do.
 
#19
Two things,

First - fasteners are hardened and HSS won't always work (easily), especially on the good fasteners like Holo-Krome. Carbide is your friend here. You want hardened dog-points so they don't mush as you tighten them. Mind you, for the size of your lathe, this probably isn't a problem.
Second, you can fashion a poor-man's tool-post grinder by putting a die-grinder in a large boring bar tool holder, or as you mentioned earlier, simply chucking the fastener in a drill and running it up against the bench grinder. You can also get away with mounting a pencil grinder and taking it very slowly. I re-ground one my my chucks this way.

Torin...
 

John Conroy

Well-Known Member
Premium Member
#20
A lot of the projects I do require me to shorten or modify screws and bolts. As Torin said, carbide insert tooling makes this job easy. Over the years I have made a series of threaded holders for fasteners of various sizes. They are made from 1.375" round hot roll. I make the depth of thread in the tool the same as the size of the fastener, for example the 3/8" tool has threads 3/8" long. They hold the fasteners securely using the clamping force of the lathe chuck and work great. Here are some pictures, they are pretty simple to make, I use a slitting saw in the mill to make the cuts. The single saw cut seems to work just as well as the more time consuming 3 sided cut. In the last pic I am preparing to make a dog point from a cup point M8 set screw. I didn't take a pic of the finished product but it was a piece of cake with the right tool to hold the screw without damaging the threads.