Q about work holding screws

S

SE18

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I'm halfway done making a mill attachment for lathe. I know the best one is T slots but I may have to wait to try that method.

Instead, I'm going to drill and tap 1/2-13 holes on the attachment steel, which is about 1" thick. I don't have a bottom tap or plug tap, but I could try drilling almost thru the steel and then tapping most of the way down.

Or, I could drill all the way thru and tap all the way through.

The purpose is for bolts to go there and on the outside have nut or clamp attachments for the work.

So my question is simple. Drill and tap all the way through the steel or drill and tap most of the way through? Which way would hold the work more securely, or, does it even make a different?

I'll try and view this post tomorrow for some responses. If I wasn't clear, I'll then try my hand at drawing what I'm describing, although I'm not a good artist.

DaveV
 
it really won't make a difference strength wise whether the thread is into or straight through the block. Just as long as your thread fit isn't sloppy. Your strength will come from the bolt grade and length of thread engaged. I would just go all the way through if possible. This will make it easier to use one length of bolt for different size pieces to be milled and if you have the room on the back you could always throw a nut on there to be doubly sure the stud won't back out. Also a through hole will give you a chance to blow the swarf out that is inevitably going to get in there. Try digging out your follower rest holes and you'll know what I mean :-)
 
Generally speaking, the depth of a hole should be 1.5 times the diameter of the bolt. This is a very high-level approximation and many factors are involved but, it's a half-decent guideline for general purpose work.

So, for a 1/2" dia bolt, the hole should facilitate 3/4" of full thread engagement.

BTW: Blind holes are kind of a pain so I avoid them when possible.

Ray
 
Tap them through and lots of them, if you have a part that doesn't set level you can put bolts in from the back to level it , just like screwjacks .
 
Ray C is on the mark with his advice. For example, look at the thickness of a 1/4" nut compared to a 1/2" nut. A hole tapped much deeper than the thickness of the nut doesn't provide any stronger connection in steel when torqued properly, it's overkill.:))
 
thanks, I made swiss cheese out of some hot rolled last night 7" X 7" with 20 holes, 1/2X13 . The steel was a bit over 3/4", not 1" as I said, having measured it. I used cutting fluid and when I got to the last few holes, it seems the tap got harder to use. I'm hoping this was due to my own fatigue and not the tap being dulled by the material. I believe the tap is American made as I purchased it second-hand, actually third hand. I used a lever from a car jack b/c after a while my body got pretty tired of tapping. I did it all with carefulness and backed up about 1/3 of every complete turn.

I've only tapped once or twice before and then for just miniature screws so this is my first big foray into big taps. I'm surprised I didn't break the tap as I always hear so many stories.

So my mill attachment is done. I did it around midnight last night so too tired to test it. Will have to await the weekend and I'll do up a post here showing it in machine accessories category right next to this one.

It's pretty amaturish looking, as the drill slipped when starting a couple of the holes so they're not aligned like a military formation. I know that will upsdet the purists. I did use a punch.

As an aside, I predrilled with 1/4" drill and the tap drill I used was 27/64 or 29/64, I can't recall, but I believe the latter. I'm not used to drilling thru steel, but the big bit went thru it real easily, which surprised me. I used a slow speed on the big bit and a faster speed for the small bit.

Another thing that surprised me is the amount of swarf and the distance it went flying==all the way across the garage. I put on gloves after a piece whipped into my hand that was steadying the steel. But what can you expect from beginners like me except nonsense.

Dave
 
Congrats! You'll find that some holes drill/tap very easily and some you struggle with a bit. The density of metal is not perfectly uniform -if it were, we wouldn't spend so much time balancing things. Anyhow, when you hit those dense spots, you struggle a bit. Also, if the tap is not straight in-line with the hole, it gets very difficult to turn and this is where most taps get broken.

So, you going to show us a picture?



SE18 said:
thanks, I made swiss cheese out of some hot rolled last night 7" X 7" with 20 holes, 1/2X13 . The steel was a bit over 3/4", not 1" as I said, having measured it. I used cutting fluid and when I got to the last few holes, it seems the tap got harder to use. I'm hoping this was due to my own fatigue and not the tap being dulled by the material. I believe the tap is American made as I purchased it second-hand, actually third hand. I used a lever from a car jack b/c after a while my body got pretty tired of tapping. I did it all with carefulness and backed up about 1/3 of every complete turn.

I've only tapped once or twice before and then for just miniature screws so this is my first big foray into big taps. I'm surprised I didn't break the tap as I always hear so many stories.

So my mill attachment is done. I did it around midnight last night so too tired to test it. Will have to await the weekend and I'll do up a post here showing it in machine accessories category right next to this one.

It's pretty amaturish looking, as the drill slipped when starting a couple of the holes so they're not aligned like a military formation. I know that will upsdet the purists. I did use a punch.

As an aside, I predrilled with 1/4" drill and the tap drill I used was 27/64 or 29/64, I can't recall, but I believe the latter. I'm not used to drilling thru steel, but the big bit went thru it real easily, which surprised me. I used a slow speed on the big bit and a faster speed for the small bit.

Another thing that surprised me is the amount of swarf and the distance it went flying==all the way across the garage. I put on gloves after a piece whipped into my hand that was steadying the steel. But what can you expect from beginners like me except nonsense.

Dave
Click to expand...
 
oh, forgot to say, I never thought about the screw jack bit. Now I have to see what kind of work-holding devices are out there. I think there are quite a few like step blocks I might try making. I imagine some types are pretty ingenious. I'll have to search the web as well. I already know I can attach my vise to the steel as the slides match 2 rows of the bolts.

My main concern will be the testing this weekend. If it moves around with light cuts, then I'm screwed (in a manner of speaking) and will have to put out a call for help.
 
Hi Ray, I noticed too when drilling it went quick in spots and slowed in others.

I'll be titling it, my $65 mill attachment (different title than my $50 mill attachment which was mostly made of wood about a month ago :-0 )

yes, there will be plenty of pictures
 
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