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Spot Facing With Slot Drill?

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Michael Gilligan17/05/2020 18:49:45
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Posted by Ron Laden on 17/05/2020 17:07:13:

Sorry for the war and peace explanation but its the best way I could explain it.

Ron

.

Nice description, Ron yes

... I’m sure it will become a point of reference next time somebody needs ti make one.

MichaelG.

not done it yet17/05/2020 20:20:32
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Don’t do it like that next time, Ron.

Get yourself the Stevenson’s blocks - both square and hex -‘cos they are a real help, with all sorts of jobs.🙂. I got extra nuts for mine as they come in handy if one needs to swap cutting tools (like drilling, threading, counter -boring or -sinking, and chamfering all in the one position. I only have one of the more expensive bearing-type nuts (at the moment) but that is always the favourite as first choice.

Ron Laden18/05/2020 05:28:18
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Yes I do need to get them ordered, ARC do a square and hex as a set.

Wanting to get the tool made I needed something hence the small alu block I made up, it did work well enough though.

Michael Gilligan18/05/2020 06:10:30
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Posted by Ron Laden on 18/05/2020 05:28:18:

[…]

Wanting to get the tool made I needed something hence the small alu block I made up, it did work well enough though.

.

... and credit to you for that, Ron yes

MichaelG.

Alan Charleston18/05/2020 07:19:23
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Hi Ron,

I'm not clear as to how you milled the teeth. From your picture, I can see that the bottom of the cutter is in the same plane as the angled part of the tooth but the side of the cutter doesn't line up with the part of the tooth which is parallel to the drill. If the teeth were cut as shown, wouldn't you end up with a negative rake? Did you file the side of the tooth after milling to give a neutral rake?

Regards,

Alan

Sorry Ron, I've looked at your post again and I see you say you filed the cutter after hardening to sort the rake out. I initially thought you meant you had filed the top of the teeth to provide clearance after milling the top of the teeth to ensure they were all the same height.

Alan

Edited By Alan Charleston on 18/05/2020 07:30:11

Dr_GMJN18/05/2020 08:05:48
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Posted by Alan Charleston on 18/05/2020 07:19:23:

Hi Ron,

I'm not clear as to how you milled the teeth. From your picture, I can see that the bottom of the cutter is in the same plane as the angled part of the tooth but the side of the cutter doesn't line up with the part of the tooth which is parallel to the drill. If the teeth were cut as shown, wouldn't you end up with a negative rake? Did you file the side of the tooth after milling to give a neutral rake?

Regards,

Alan

Sorry Ron, I've looked at your post again and I see you say you filed the cutter after hardening to sort the rake out. I initially thought you meant you had filed the top of the teeth to provide clearance after milling the top of the teeth to ensure they were all the same height.

Alan

Edited By Alan Charleston on 18/05/2020 07:30:11

If the cutter moves right to left, and the back of the cutter is on the centreline if the part, wouldn’t it simultaneously form a zero rake tooth face and the angled part of the tooth in front? So in the picture it’s cutting the tooth that’s facing us on the left, and the sloping bit of the tooth in front looks like a horizontal line. Then locally file the ramp just adjacent to the face of the tooth. That’s how I understood it.

Edited By Dr_GMJN on 18/05/2020 08:07:20

Ron Laden18/05/2020 08:09:02
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Posted by Alan Charleston on 18/05/2020 07:19:23:

Hi Ron,

I'm not clear as to how you milled the teeth. From your picture, I can see that the bottom of the cutter is in the same plane as the angled part of the tooth but the side of the cutter doesn't line up with the part of the tooth which is parallel to the drill. If the teeth were cut as shown, wouldn't you end up with a negative rake? Did you file the side of the tooth after milling to give a neutral rake?

Regards,

Alan

Sorry Ron, I've looked at your post again and I see you say you filed the cutter after hardening to sort the rake out. I initially thought you meant you had filed the top of the teeth to provide clearance after milling the top of the teeth to ensure they were all the same height.

Alan

Edited By Alan Charleston on 18/05/2020 07:30:11

Hi Alan,

No it is as you thought, when you turn the block through 90 degrees the cut runs through the previous cut with the edge of the tool creating the face of the tooth which is neutral. In hindsight I probably didn't need to dress the top of the teeth but in doing so it left flat spots on top of the teeth and it was those that I filed a small relief to. So my teeth have a neutral face and a relief on top or bottom if you like.

I don't know if Jason leaves a neutral face but I,m sure he will confirm.

JasonB18/05/2020 09:00:12
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Yes just a zero rake face left by the edge of the tool seems to work OK, you could use a triangular file to add soem positive rake or even use a dovetail type cutter to do the same.

First cut and the edge of the tool forms the first cutting face.

spot1.jpg.

spot2.jpg

Next cut forms the clearance and you get the cutting edge where they meet

spot3.jpg

Ron Laden18/05/2020 09:14:12
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Thanks for that Jason far better than I was explaning it.

Dr_GMJN18/05/2020 11:09:38
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And the CAD is a left/right mirror image of Ron's photo presumably?

JasonB18/05/2020 11:16:19
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That's a reverse spot facer for those that don't want to run in reversewink 2

Conventional would end up like thisblush

spot4.jpg

John Baron18/05/2020 11:26:31
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Posted by Dr_GMJN on 17/05/2020 16:01:35:
Posted by Hopper on 17/05/2020 02:54:09:

What rpm did you run that cutter at? You cant use HSS speeds with silver steel. Try taking it nice and slow on that cast iron hard skin. Maybe like 400 rpm or so. Or even less to start with.

Edited By Hopper on 17/05/2020 02:55:03

Hopper, to be honest I was running at a lot more than 400rpm. But t's irrelevant; I made a mistake (or at least trusted a years old storage label) and used, I think stainless - it's not magnetic.I should have at least checked before, but lesson learned.

I am ordering some silver steel and a few other bits later today from M-Machine, and will make new storage boxes and mark the pieces with fet tip. I will try again when I get them, and hopefully it will work.

If its silver steel / drill rod, once you have got it to red heat and quenched it it will be glass hard ! If you use it like that without tempering, make sure that you wear safety specs.

Dr_GMJN18/05/2020 11:34:12
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Posted by JasonB on 18/05/2020 11:16:19:

That's a reverse spot facer for those that don't want to run in reversewink 2

Conventional would end up like thisblush

spot4.jpg

Yes, that was my understanding - one pass of the cutter right to left forms everything.

I'm going to try that method when I get the steel.

If I make a fixture like Ron's, any tips for marking out the rotation positions on the steel shaft ie 0, 90, 180, 270?

Is there an optimum number of cutting edges to reduce vibration?

Thanks.

Dr_GMJN18/05/2020 11:35:27
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1230 forum posts
Posted by John Baron on 18/05/2020 11:26:31:
Posted by Dr_GMJN on 17/05/2020 16:01:35:
Posted by Hopper on 17/05/2020 02:54:09:

What rpm did you run that cutter at? You cant use HSS speeds with silver steel. Try taking it nice and slow on that cast iron hard skin. Maybe like 400 rpm or so. Or even less to start with.

Edited By Hopper on 17/05/2020 02:55:03

Hopper, to be honest I was running at a lot more than 400rpm. But t's irrelevant; I made a mistake (or at least trusted a years old storage label) and used, I think stainless - it's not magnetic.I should have at least checked before, but lesson learned.

I am ordering some silver steel and a few other bits later today from M-Machine, and will make new storage boxes and mark the pieces with fet tip. I will try again when I get them, and hopefully it will work.

If its silver steel / drill rod, once you have got it to red heat and quenched it it will be glass hard ! If you use it like that without tempering, make sure that you wear safety specs.

I was tempering by getting it yellow-ish and re-quenching in brine.

JasonB18/05/2020 12:11:34
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You should not really need to do any marking out.

Having the round embryo tool in a square block gives you the 90degree spacing simply by turning the block so that the next face is against the fixed jaw.

Having the edge of the cutting tool on the workpiece centre line is important but as you gave a DRO you should locate the back or front of the rod and zero your Y reading then locate the opposite face and half the reading to give the ctr line. Then just move the spindle so that it is half the tool diameter away from zero in the Y axis

Provided the block is held at the same height and angle then the tool height is not critical and the first cat can go beyond half way in the X direction as by the time the last cut has been taken all edges will be at the same height.

I hardly ever temper these type of tools or form tools and have not had one break.

Ron Laden18/05/2020 13:23:42
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I havnt tempered mine either, I didnt think it a worry on a slow running spot facer.

I ran it at 375 rpm and it cut nicely.

Dr_GMJN18/05/2020 22:19:37
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I've found some round aluminium that I think I could make into a fixture:

I'd mill four flats on the sides.

I'd use one of the vice clamps I made last week, to give me the angle (14.5 degrees): It would rest on the vice slides so that it could only fit in one position. The flats on the aluminium are wider than the vice clamp.

I'd press a piece of turned bar into the 6mm clamp hole to form a spigot for the aluminium.

The tool blank would fit in a 10mm hole in the aluminium, and be secured with a grub screw.

I'd get a 0.7mm tooth height.

Have I understood Ron's concept correctly?

Does the tool tip need more support?

Thanks all.









JasonB19/05/2020 07:07:19
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Should be OK, you could use a slightly shorter pin so the 10mm hole can go a bit deeper which would help.

Ron Laden19/05/2020 07:47:01
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Just a couple of thoughts I think Jason said 6mm diameter is about right for a 7BA spot face. If you had some 6mm silver steel you could make the complete tool from it. Cut the teeth on the end of a piece of 6mm having first drilled the alu block 6mm and size the length of the tool to allow it to protrude through the bottom of the alu block as a spigot. That way you wouldn't need to make and fit a spigot in the clamp block.

Also you are showing a very deep hole for the pilot and on your first attempt the pilot looked very long protruding out of the tool. Maybe you did that for a reason but on mine I made the pilot 14mm long drilled the tool 10mm leaving 4mm protruding.

I am not criticising just offering some thoughts.

Ron

Edited By Ron Laden on 19/05/2020 07:51:38

Edited By Ron Laden on 19/05/2020 07:53:00

Dr_GMJN19/05/2020 08:11:08
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Jason, Ron, thanks for the comments.

I have already ordered 10mm silver steel (along with some other samples), which is due to be delivered today.

I was thinking after reading Jason's comment that I could turn a small 6mm spigot on the bottom of the tool blank, to fit in the clamp hole. That would give me less overhang - and eliminate the pin as you say Ron.

The central hole isn't representative depth, but I agree the protrudung spigot was a bit long. I will make another (I wasn't particulalry happy with the finish anyway).

I made the spot face diameter 5.5mm so it didn't cut too far into the adjacent block fillet radius. If it doesn't clean up at that, I'll try 6mm.

Thanks.

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