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Jumpcannon
12-24-2010, 02:54 PM
I am drilling a .868 thru hole in 1018 steel 1" thru. Currently i am center drilling, then pilot drilling with a 1/2, then using a 3mt 55/64th drill. I would like to speed this process up as much as possible. What are my options with a 1hp lathe? Is there any drill i can use that is self centering and runs true? Thanks for any feedback.

ENTERPRISE LATHE
12-24-2010, 03:01 PM
I don't know how long your drill bits are but maybe try using a jobbers length
drill bit. Screw machine drill bits are the same length I think. Since they have a shorter over all length they won't walk so much. Hope this helps

becksmachine
12-24-2010, 03:56 PM
You say your lathe has a 1 hp motor, it would also be helpful to specify what speeds are available and which speed you are trying to use? ;)

Dave

Jumpcannon
12-24-2010, 04:03 PM
You say your lathe has a 1 hp motor, it would also be helpful to specify what speeds are available and which speed you are trying to use? ;)

Dave
speeds range between i would like to do this between 300 and 600 rpm.

Oldbrock
12-24-2010, 04:18 PM
After center drilling you should use a pilot drill of a diameter that equals the width of the chisel point of the finished size drill. If you want to eliminate the center drill you can bring the back end of a toolbit to touch the pilot drill as it touches the work and it wiill hold it on center as you start to drill. Then you can retract the "steady" as you drill through. Peter

Black_Moons
12-24-2010, 04:26 PM
Id consider going even slower for the final drill if you have a decent backgear. You would be amazed how much metal a 3/4" drill can remove at 200rpm given enough tailstock pressure and torque... The chips tend to clear out nicely if you can get them to be one solid chip that snakes up the flutes, No peck drilling needed.

of course, I have allready replaced my 2" long tailstock under clamp with one thats uh, 10" long... Mainly so it would stick out BEHIND the tailstock, incase I needed to add a second bolted clamp ontop of it (Camlock tailstock, but after I reduced the cam travel to 1/3rd what it was, and made the clamp 5x longer, it now HOLDS), Otherwise my tailstock would move out as much as the drillbit went in.

Also when I made my tailstock clamp, I made the clamping surface with a 'poor milled finish' to help get more traction. (Gives little grooves for the oil to get outta the way)

beckley23
12-24-2010, 04:45 PM
Drill a through hole using a 3/16, or so, screw machine drill bit and then go through with the 55/64. You may want to try a 55/64" screw machine drill bit only, but I think you're going to have HP issues. No need for center drilling, just make sure the inital drill bit stabilizes, before really going to it. You will want about 100 SFM for both drills, and use coolant.
Harry

Mcgyver
12-24-2010, 04:48 PM
Use a spot drill, not a centre drill....in theory a well done split point might bypass the spotting stage but i doubt it. Like BM says, slow down for big drills.....I doubt 1hp has the umph for high rpms. As for drills running true, thats a function of how well they're ground

you can get pretty quick at it, spot, pre drill maybe 1/4" at high speed, drop the speed load the big drill....there's not a minute's work there and you're onto the big drill

Jumpcannon
12-24-2010, 04:49 PM
Drill a through hole using a 3/16, or so, screw machine drill bit and then go through with the 55/64. You may want to try a 55/64" screw machine drill bit only, but I think you're going to have HP issues. No need for center drilling, just make sure the inital drill bit stabilizes, before really going to it. You will want about 100 SFM for both drills, and use coolant.
Harry
excellent...thanks!

Arcane
12-24-2010, 04:50 PM
If your holding that bit in a morse taper in the tailstock, don't be afraid to use a lathe dog to take the brunt of the torque. It will prevent the drill from spinning in the MT socket and galling either the drill taper, the socket or both. Just a reminder...:)

Willy
12-24-2010, 04:52 PM
One extra thing to bare in mind if you are pushing some big drill bits hard while using the tailstock.

Tailstocks are not really designed to transmit huge amounts of torque through the key that keeps the quill from turning.
With a 1 hp lathe I would think that the quill and key are not that heavy.

If your are going to take aggressive cuts you may want to consider using a dog to transmit the torque rather than letting the quill key take all the load.

Edit to add....Arcane is faster with his trigger finger than me!

KiddZimaHater
12-24-2010, 04:54 PM
Do you have access to a drill press or mill?
If it's just a simple drilling job, then drilling holes is ALOT easier and faster on a drill press or mill, then on a lathe.
I clamp my 3-jaw chuck on the mill table, find center, spot, and drill away.
Sure beats cranking away on the tailstock.

tmc_31
12-24-2010, 05:18 PM
Jump,

I have a similar project to do (I hope). I will be drilling a 7/8" hole through 1" of A36. I ran the problem through my Machinist Toolbox (software). It spit out:

Surface Speed:75FPM
Spindle Speed: 327RPM
Feedrate: .8829IPM

I believe the horsepower requirement is about .5HP

I plan to use a .875 MT3 (usa made HSS) drill and machine drive it with the carrage using a MT3 tool holder in my QCTP (tool holder has a slot for the tang). Will use flood cooling. (I have 50 to do)

My machine is 2HP. I plan to center drill it then do it in one shot at 7/8.

Jumpcannon
12-24-2010, 09:52 PM
Jump,

I have a similar project to do (I hope). I will be drilling a 7/8" hole through 1" of A36. I ran the problem through my Machinist Toolbox (software). It spit out:

Surface Speed:75FPM
Spindle Speed: 327RPM
Feedrate: .8829IPM

I believe the horsepower requirement is about .5HP

I plan to use a .875 MT3 (usa made HSS) drill and machine drive it with the carrage using a MT3 tool holder in my QCTP (tool holder has a slot for the tang). Will use flood cooling. (I have 50 to do)

My machine is 2HP. I plan to center drill it then do it in one shot at 7/8.Excellent idea! I may try that route also!

tmc_31
12-25-2010, 02:04 AM
Let us know how it works out for you!!

In addition to drilling that hole, I am going to have to tap it to 1"-8tpi. Since I have so many to do, I thought I would give power tapping in the lathe a try. The lowest speed on my lathe is 70 RPM.

Good luck with your project,

Tim

Black_Moons
12-25-2010, 03:20 AM
I don't like using my carriage for big drills ever since my toolpost rotated in the middle of drilling something -_-; Maybe the nut wasent tight enough, But it left a bitter taste in my mouth... And a very bellmouthed hole (was at the very start of drilling the hole)

Andrew_D
12-25-2010, 12:59 PM
If your holding that bit in a morse taper in the tailstock, don't be afraid to use a lathe dog to take the brunt of the torque. It will prevent the drill from spinning in the MT socket and galling either the drill taper, the socket or both. Just a reminder...:)

Excellent suggestion!

I've done this quite a few times with drill bits over 1". I brace the lathe dog's tail against the compound slide. Might brace against the cross slide or carriage for a smaller lathe.

Andrew

tmc_31
12-25-2010, 03:18 PM
I don't like using my carriage for big drills ever since my toolpost rotated in the middle of drilling something -_-; Maybe the nut wasent tight enough, But it left a bitter taste in my mouth... And a very bellmouthed hole (was at the very start of drilling the hole)

Hey Black Moons,

Did the toolpost rotate, or was it the compound? I also am concerned about this. My compound has a spring loaded locater pin that mates up to a hole in the toolpost to keep the toolpost from spinning. I am more concerned about the compound rotating on my lathe. The original bolts holding the compound down were very soft and stripped out quickly. I replaced them with better bolts and nuts (I hope) but am still concerned. If it tries to rotate, I guess I will drill from the tail stock and tie the carriage and tail stock together.

Jumpcannon
12-27-2010, 06:01 PM
No lathe dog is necessary. I pilot drill first with a 1/2" at 720rpm then use the .868 drill and run it at 350rpm. Cuts like butter and is very quick. Did this all from my tailstock. After that i face the piece which is 3 3/8th round and ran it at 600rpm and .007ipr. Beautiful finish and knocked my time down 50%. I run about 50 parts at a time like this.

becksmachine
12-27-2010, 06:48 PM
Do you think that you do not have enough horsepower to eliminate the pilot drill operation?

Or are you afraid of the amount of thrust required?

Dave

Jumpcannon
12-27-2010, 10:44 PM
Do you think that you do not have enough horsepower to eliminate the pilot drill operation?

Or are you afraid of the amount of thrust required?

Dave
Actually i havent even thought of it. I probably could do it without pilot drilling. I wonder if that large drill would walk any? Probably very minimal. I will try it next time i do these.

PixMan
12-27-2010, 11:04 PM
I wonder if any of you have ever tried using an insert tool for short-depth holes such as these under discussion. I've got a couple of different sizes of the Valenite Center Dex tools, and have enjoyed great success using them not only as milling tools, but as center-cutting drills.

They make a lot of different sizes and a couple different lengths of them, ranging from single-insert cutters cutting a .48" x 1" deep to a "2 x 2" to a 1.75" x 3.5". I have the .73" x 1", and a 1.0" x 1.25".

They accept coolant thru (if you're so inclined to plumb it), and since they're essentially a single flute drill they don't use a lot of power. I have used both on dad's 1HP Bridgeport without issue, but on the Taiwanese 5HP lathe (really more like 4.2 US HP) the machine isn't even breathing hard.

If anyone is near me or is willing to pay shipping, you're welcome to try it. This is the 1" x 1.25" version, SVMSP 100R 90CCC. It has a 3/4" Weldon shank that I can hold in our QCTP's No.4-41 boring bar holder (with bushing.)

http://img.photobucket.com/albums/v466/kenm10759/Tools_4_sale/IMG_0691-r.jpg
http://img.photobucket.com/albums/v466/kenm10759/Tools_4_sale/IMG_0699-r.jpg

Jumpcannon
12-28-2010, 12:02 AM
I like the looks of that! Will that thing drill without pilot drilling first? I guess the inserts would have to be offset to do that.

airsmith282
12-28-2010, 12:21 AM
personly if it does not have to be a fine finish inside and absolet perfect size as we all know drills go over or slightly under then just center drill it then use the bit you need for the full size use 200 to no more then 330, but not below 200 rpm and feed it in slow and lots of cutting fluid and you should be fine, works for me , i do belive in step drilling cause it dont work worth a crap ,but you can also drill a hole just big enought to fit a borning bar in then bore it out to the size needed lots of custting fluid and about 200 to 250 rpms is just fine borning at 300 and above might be ok , but take very small bites cause borning bars flex alot and you dont want to bore tapers ,,,

tmc_31
12-28-2010, 03:23 AM
PixMan,

Those look pretty cool. Have you tried them under power, or have you just been hand feeding them? Where do you get them and what do they cost?

Tim

PixMan
12-28-2010, 08:13 AM
I like the looks of that! Will that thing drill without pilot drilling first? I guess the inserts would have to be offset to do that.

The inserts are offset. In the bottom photo yu can see the one on the right comes across the center, the one on the left is the "outboard" insert that determines effective cutting diameter.

The Centerdex tools are self-centering, but can walk a bit until you get past the insert's radius. You need a rigid setup to use them, but no pilot drill or center drill.

WHen I use it it the Bridgeport as a drill, end mill or face mill it's all hand feed. Using as a drill, you position the X-Y slides to put the tool on the center line you need, then lock them. I have fed down by hand with no problem, but prefer to set the feed at .0015" per rev and engage the clutch. The power feed on the BP did protest when I tried a 316SS block, but it cut by hand just fine.

On dad's lathe it's got enough power that it never blinked, but the key is using a light feed so the toolpost doesn't twist around. I got the best results with the compound at 90, but that shouldn't matter.

As for cost, well I have 28 of them left that I was selling on Ebay for $45, shipped. ;) I have a dear friend who recently retired from Valenite (now Walter) and found these in his garage. Still a current product and been in the catalog for over 30 years. Lists for $125. In the home shop and used gently, the inserts seem to last forever. (Doesn't come with any of them though.) If you search for Center Dex in "completed listings" you might find my listing.