Spot Facing With Slot Drill?

[JasonBModerator @jasonb]

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 LadenParticipant @ronladen17547]

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_GMJNParticipant @dr_gmjn]

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.

[JasonBModerator @jasonb]

Should be OK, you could use a slightly shorter pin so the 10mm hole can go a bit deeper which would help.

[Ron LadenParticipant @ronladen17547]

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_GMJNParticipant @dr_gmjn]

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.

[Ron LadenParticipant @ronladen17547]

Posted by Dr_GMJN on 19/05/2020 08:11:08:

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.

Good idea, that would work.

Ron

[Anonymous]

Good grief, this all seems way over-complicated. It should be possible to make a working spotface cutter using a file to cut the teeth. The fundamental question is why didn't the orginal spotfacing with a slotdrill work as expected? If it's a problem with the setup, milling machine or technique it needs to be bottomed out rather than covered up.

Andrew

[Ron LadenParticipant @ronladen17547]

Andrew, you probably have a point there with regard to making them with a file, Jason mentioned thats the way he sometimes does them but I would have thought it a good little project for someone new to a mill.

I made mine on the lathe and mill quite simply because I enjoy making bits of tooling, thats my excuse anyway.

Ron

[Dr_GMJNParticipant @dr_gmjn]

Posted by Ron Laden on 19/05/2020 12:15:07:

Andrew, you probably have a point there with regard to making them with a file, Jason mentioned thats the way he sometimes does them but I would have thought it a good little project for someone new to a mill.

I made mine on the lathe and mill quite simply because I enjoy making bits of tooling, thats my excuse anyway.

Ron

Exactly.

Plus, if I thought making a simple jig to hopefully get more consistent results from a new technique to me was over-complicated, then I certainly wouldn't be attempting to make a steam engine from a set of castings and bits of bar.

[Anonymous]

The teeth on this counterbore were filed by hand, but they still did a precise job on the part shown:

In the holes can just be seen a hollow spigot that will hold a wing valve. The spigot is counterbored so that it stands proud from the outer shell.

Andrew

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