Improving Drilling Accuracy after Center Punching

Probably old hat to many but I just tried this method and I must say that it works and works well.
The holes are in a base plate that has limited room for error since I did not want to drill out the sides
of the vise that the base was to be used on. It was a casting so it was not exactly symmetrical.

I did not center drill any of the holes after I center punched them.
Instead I used a 1/2" center in my drill press chuck and lined up each hole prick with the center point.
Locked the base down to the drill press table with a toggle clamp for each prick point.
Then I changed out the center for the drill bit without center drilling. Went straight to the #21 drill bit.

All the holes were drilled and then the newly drilled base was aligned to the bottom of the vise.
The base was then used as a template and the holes were drilled into the vise cast iron frame.
Drilling was exactly where expected and none of the holes broke through the sides of the vise.
The drill bit used was a #21 which was the tap drill for the 10-32 threads that needed to be tapped.

The rest of the story is in my next project: Locking Down The Vise
http://www.homemadetools.net/forum/r...905#post105773

Cheers, JR

JR,
Excellent technique and explanation. I have used the same method with a "sacrificial" over-plate clamped on the part and preserved the exact very close-to-the-edge alignment without any break-through. You have to trust the method.
Thank you for the posting.
Regards,
Paul

Thanks Paul, good to know that other workers have used a similar method.
I know in the past when prick punching and center drilling without anything lining things up that my results were
often close but not right on. This method really works. Using the clamp helps too.

Cheers, JR

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For a bit more accuracy in this technique, I use the pointy end of a double-ended edge finder in place of the 1/2" center. A fingernail dragged across the junction where the point meets the body of the edge finder can detect the tiniest deviation.

I use the same technique to center over holes, both small and large...

http://www.homemadetools.net/forum/h...ring-aid-26216

How do you use the slots in the drill press table? Can you show me
with photos? Thanks, douglas

Sure can. T-slot nuts are available from Littlemachineshop.com and any machining equipment supplier. Many on line and even Ebay.
Here are a few pics of the details.

As you can see I have also drilled and tapped mounting holes in my drill press table. Mostly for some jigs that I use from time to time.
T-Slots are more versatile.

Cheers, JR

Thanks I have to get some I had the drill press for years but never
knew what the slots were for. Thanks, douglas

You are very welcome Douglas, if you don't have a drill press vise yet then you may consider one of them.
Two types are inexpensive and very useful on the DP. One has slots that you can use with the T-Slots and bolts to fasten it to the DP table.
The other one uses slots in it's side for clamping. It can be used in the horizontal or vertical mode.

I have included a picture of the side clamping type below. It is mounted on a mini mill. You can't see the T-slots since the mill has been fitted with table covers in that picture.

Cheers, JR

Just added a second picture showing the slots better. You can see how it could be used in the vertical position on the DP.

Thanks, I have a couple of nice DP vises, I wondered what the slots were for. The machine tool company
you referred doesn’t carry 916” slot nuts, must be an oddball size? I wish I knew how to post a link,
I found an alternative nut that might work. Its a flat bar about 1” L x 1/2” W x 1/8” thick with a 1/4-20
female thread in the middle. Thanks douglas

Quote:

---

Originally Posted by Douglas Rome

The machine tool company
you referred doesn’t carry 916” slot nuts, must be an oddball size?

---

MSC has them...

https://www.mscdirect.com/product/details/73154338

For light duty, it's possible to make a serviceable T-bolt from a carriage bolt; just grind the head to fit the T-slot.

Douglas, try this link to McMaster-Carr....They have just about everything.

https://www.mcmaster.com/#t-slot-nuts/=1b9sgo9

Dimensions are listed.

Cheers, JR

Thanks Marv, excellent reminder for the carriage bolt mod. I have made a few of them in the past.

Douglas, I was on the LMS site this morning and did a search on T-Slot-Nut and found the 7/16 and quite a few other sizes.
https://littlemachineshop.com/produc...rm=t-slot-nuts

The also list a 7/16 slot cleaner which is easy to make and cleans out all the swarf not just the steel!

Cheers, JR

I was about to order 4 9/16” slot nuts from MacMaster, I think about 12bucks,
nowhere on their website did it say how much shipping was, I had to call them!
Turns out they wanted $6 to mail, so I declined. Too much for a little shipping
envelope. Thanks douglas

Attachment 21799

Here’s what I ended up ordering.
Thanks. Douglas

If you are using 3/8-16 bolts then LMS has 1/2" T-Slot-Nuts that may work ok in your 9/16 slots.
Only $1.49 each and they usually ship small orders by mail. I have had shipping as low as $3.00
from them on a small order.

https://littlemachineshop.com/produc...2021&category=

Cheers, JR

Quote:

---

Originally Posted by Douglas Rome

Attachment 21799

Here’s what I ended up ordering.
Thanks. Douglas

---

Ok, I posted prior to seeing your post. Those are light duty but should work in low stress applications.

Cheers, JR

I plugged in qty 4 in LMS and their lowest was 1st class mail $4.45. Thanks, douglas

Quote:

---

Originally Posted by Douglas Rome

Attachment 21799

Here’s what I ended up ordering.
Thanks. Douglas

---

I got them a couple days ago. They are “tiny”, too tiny to use, we’ll see.
Thanks. Douglas

Well that is unfortunate. If they are large enough so they don't rotate in the slot you
could use a washer on each one that would be large enough not to pull thru the slot?

I suppose another quick fix would be to solder the washer to the "nut" placing the washer
above the nut? Light duty but might work in a pinch.

Cheers, JR

The Amazon description for those nuts says...

7/16" wide by about 1" long

so, obviously, they won't work in 9/16" wide T-slots.

Another thing to consider... Real T-nuts are not threaded all the way through. This is to make it impossible for the stud to emerge from the bottom of the nut, touch the bottom of the slot, and begin jacking the T-nut up against the bottom of the ledges. If this happens and enough force is applied the T-slot can be broken. If you ever get T-nuts that are fully threaded, use a chisel to damage the bottom threads so a stud can not pass all the way through.

If real T-nuts are too pricey for you, try buying some carriage bolts with a head diameter greater than 9/16" and grinding them to fit into the T-slots.

These Amazon things will work in a pinch, I just have to take more care installing them.
The real slot nuts are not expensive, it’s the shipping price that I take exception to.
Thanks. Douglas

Excellent points to all. One thing to remember with the thin flat "nuts" like Marv pointed out is the risk of
putting pressure from the base of the table to the top of the T-slot and breaking it out.

Back to the shop.

Cheers, JR

Quote:

---

Originally Posted by Douglas Rome

These Amazon things will work in a pinch, I just have to take more care installing them.
The real slot nuts are not expensive, it’s the shipping price that I take exception to.

---

Have you searched Amazon for T-nuts? For example...

https://www.amazon.com/dp/B009SWGFB4/ref=biss_dp_t_asn

Many of their offerings have free shipping on orders of $25 or more. Given the scope of Amazon products, putting a $25 order together should be easy.

Aside: Many of the one-star reviews on the T-nuts complain that the threads do not go all the way through the nut. I can't understand why people buying such a specialty item wouldn't understand that they're supposed to be that way.

I got these 1/4s free shipping. I agree, thru thread is the only way. I couldn’t find 9/16 on
Amazon I’ll look again. Thanks. Douglas