Turning Tool And Facing Tool Questions

[Round in circles]

Seeing how this is about grinding the tool tip , I'd like to ask a question that has been puzzling me as I seem to have a mental block about something.



I have a QCTP on my old lathe
I want to bore an inch hole through some 2.5 " x 3 " long round M/S bar & at either end of the newly made " tube " I want to open it out to take a 1 &3/4 " OD sealed roller bearing unit that is 1/2" wide.

I've given it quite a lot of thought of how to ensure that the bearing will be secured and am going to use circlips but I can't quite visualize what sort of ground tip I need to make so I can clean out the recess so it has a 90 degree face to the turned 1 & 3/4 holes internal face . ( have no problems accurately using a grind stone )
I have some rather weedy boring bars hand ground to almost an off set round with a spade type tip on the end from 1/2" sq HSS bar but the cutting end face that would be at the internal flat face of the boring is angled to about 30 degrees and as that is a the other half of a thread angle I'm loath to alter it .

Can some of you more experienced guys sketch what sort of grinds I can put on some new 1/2 " square HSS bar for me to make this cutter , as I'm not sure if a simple grind of face and angling the QCTP a tad will suffice when it hits the back wall ?

 

[JR49]

Round in Circles, not sure if I'm understanding correctly, but if I am, you can grind the 1/2 " tool so that it will go straight in like a boring bar. If you cut the little parting tool at the front perfectly perpendicular to the tool bit then, just be sure that the tool is parallel with lathe axis, and the groove will have a 90 deg. face. See my sketch, hope this helps, JR49
EDIT, if you have a boring bar that holds a 1/4" or smaller bit at 90* to the bar, you can use that and have less grinding. good luck

 

[mikey]

Let me be sure I understand you. You are going to bore a 1" through hole through the stock, then on each end you plan to open up that center bore to house a bearing on each end and hold the bearing in place with a retaining ring, right? You seem to need a boring bar that will bore a flat face at the bottom of the bearing bore.

Grinding a boring bar is not difficult but it is time consuming, especially in HSS. Personally, I would not bother. You can buy a boring bar with a 5 degree positive lead and do that bore in no time. Likewise, you can buy a grooving bar to suit the ring you plan to use and get the job done quickly and well. I'm not trying to discourage you from grinding your own tools. I saying that for me it is not worth the time and effort to do so. With that said ...

How are you planning to do the center bore? Can't you use that same bar to open up the ends?

You can grind a grooving tool like JR shows; just be sure you round the underside of the cutting edge to provide adequate clearance.

 

[Round in circles]

JR & Mikey,
I have the tool to make the circlip retaining grove .

This by Mikey ,is what I'm after " You seem to need a boring bar that will bore a flat face at the bottom of the bearing bore "

The 1 " centre bore was going to be done using MT drills in the tail stock as I have a few that will get me there .
It is indeed the flat face at the bottom of the bearing bore that I'm having mind games with .

Mikey your post has have triggered an avalanche in the old grey matter container , I think I've got it sussed using stuff I already have guys .

 

[mattthemuppet2]

you're going to really struggle to get that face flat using that boring bar. Does the other end have a hole for a hss bit at 45deg instead of 90? If so, as long as it's sticking out far enough, you'll be able to grind a bit that will do the job. You'll need some relief at the face (the side of the tool closest to the face of the bore) and I'd probably grind it with some back rake (from the tip to the boring bar) but no side to side top rake (so the top neither slopes to the left or right of the bit, looking at the tip). Make sure the front of the tool has enough relief not to rub on the side of the bore that you're starting with.

If that bar doesn't have a 45deg hole in the other end, you could make one relatively easily by milling a slot at the right angle, slitting the back of the slot and putting a pinch screw on the top (if you have clearance).

 

[mikey]

You might also be able to do this with a simple knife tool, which you probably have already. If you position the tool nearly parallel to the spindle axis but with the tip slightly toward the outside (negative lead angle) you can feed out from the center bore and stop at your desired ID, making multiple passes until you reach the desired bore depth. I do this all the time to make shallow depressions on the end of a part.

 

[Round in circles]

you're going to really struggle to get that face flat using that boring bar. Does the other end have a hole for a hss bit at 45deg instead of 90? If so, as long as it's sticking out far enough, you'll be able to grind a bit that will do the job. You'll need some relief at the face (the side of the tool closest to the face of the bore) and I'd probably grind it with some back rake (from the tip to the boring bar) but no side to side top rake (so the top neither slopes to the left or right of the bit, looking at the tip). Make sure the front of the tool has enough relief not to rub on the side of the bore that you're starting with.

If that bar doesn't have a 45deg hole in the other end, you could make one relatively easily by milling a slot at the right angle, slitting the back of the slot and putting a pinch screw on the top (if you have clearance).

I understand what you have said, sadly the bar is square at the other end ... I don't have a milling machine nor a lathe milling attachment ( pathetic aren't I )

 

[Round in circles]

You might also be able to do this with a simple knife tool, which you probably have already. If you position the tool nearly parallel to the spindle axis but with the tip slightly toward the outside (negative lead angle) you can feed out from the center bore and stop at your desired ID, making multiple passes until you reach the desired bore depth. I do this all the time to make shallow depressions on the end of a part.

Got it , I may have such a HSS knife tool that cuts at/towards the left top edge .. I may have to sculpt it a tad to give a bit more clearance as the bearing bore hole will be about 3/4 deep.

Many thanks

 

[mattthemuppet2]

you don't have to have a mill, I'm sure you could manage with a drill press (or hand drill if you have to), a saw and some files.

If the recess is only 3/4in deep you can easily grind a 3/8 square bit to do that. Looking at the front, grind the sides into a 1/4 circle (ie. the bottom right quarter of a circle) for about an inch. Then grind the same side from ~1/4 from the tip to the full inch a little more. Grind the 1st 1/4in so that the tip angles slightly at the side to meet that recess you just ground. Grind the front a wee bit, say 5deg or so, both top to bottom and left to right. Then you can grind the top for a bit of rake if you want. Stone it and you're done, easy peasy.

 

[mikey]

Got it , I may have such a HSS knife tool that cuts at/towards the left top edge .. I may have to sculpt it a tad to give a bit more clearance as the bearing bore hole will be about 3/4 deep.

Many thanks

You shouldn't have to alter the tool. Just angle the tip about 5 degrees off center. You are orienting the tool like a boring bar, with the tip pointed slightly to your left. Most knife tools should have more than enough relief under the cutting edge to make this cut and the shank of the tool will not even come close to touching the edge of that bore.