Large Concave Radius

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ML
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Re: Large Concave Radius

Post by ML » Sat Jul 23, 2011 12:26 pm

Steffin,

That style is very popular, many variations. I have seen one with two triangler bits, one facing each way, hence concave and convex. The two thoughts that come to mind; height adjustment? (if really needed?) and a bushing or bearing central pivot.

I will be interested in your descision, have fun.

Michael

Steffin T
Posts: 87
Joined: Wed Aug 11, 2010 8:07 pm
Location: Palm Springs, CA

Re: Large Concave Radius

Post by Steffin T » Sat Jul 30, 2011 5:53 pm

After a little more research, realized this is a subject that has been beaten silly... (new guy error).

The Holdridge tools are very nice but for the frequency of use, I am leaning towards making one similar to the "bedair style", with a few changes. As far as the insert style goes, which insert would most recommend to design around?

Billtodd, looking at the tool you made, is that a HSS toolbit that does the cutting... similar to an upright boring bar?

...obviously, still getting ideas, thanks.

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BillTodd
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Re: Large Concave Radius

Post by BillTodd » Sun Jul 31, 2011 7:42 am

Billtodd, looking at the tool you made, is that a HSS toolbit that does the cutting... similar to an upright boring bar?
Yes, exactly (except the cutter is a ground out from a broken carbide drill)

It was made out of odd & sods that I had laying around: The Z piece is just 12mm plates bolted together. The bearing block at the base is scrap Ally with two ball races pressed in and clamped into the bottom of the Z piece. The bar is 16mm silver steel.

The radius was pre-set by adjusting the tool position (the bender is for 7/8" tube so there's not too much overhang)

Bill
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Richard_W
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Re: Large Concave Radius

Post by Richard_W » Sat Aug 06, 2011 11:59 am

Here are a few pictures of the radius turner I built back around 1987. I had most everything burned from 1 1/4" plate. Instead of bolting it to the compound I wanted it to fit in an Aloris type holder or square turret. This was mainly to save set up time in the shop. The plate that is screwed down in the tool holder is boted to the bottom of the main frame of the radius turner. This was done so I could move it to the other side and have the frame in line with either the ways or the compound. I have used it both ways over the years. I haven't used this in about 15 years, so it naturally shows signs of neglect from sitting in a shed for the last few years. I had a straight 7/8" shaft for it, but I don't think it came back from the machine shop I loaned it to some years ago. One thing you will notice is I use round brazed carbide tools in it rather than the more common square shank tools. This was done for ease in building, since I didn't have a square 1/2" broach. On the 7/8" shank that's missing I used a 5/16" round carbide tool. You can see photos of some tools in their box in one of the pictures. As you can see all the attachments I made for it to do either bigger radiuses or to turn larger balls. Most everything should be obvious from the pictures on how I made everything including the handle. The reason for the long handle was that you could get finer feeds and have more leverage over a short handle. As a side note the handle was made from old rusty square stock I found in the scrap plie. The one thing I would have done differently was to anneal the frame before machining since it twisted slightly a few weeks later and I had to open up the hole in the bronze bushing a little for it to turn freely again. Also notice that the lower pivot is nothing but a 1/2" Allen set screw with a 60 degree point turned on it and a jam nut. This allows me to set the tool center height with just a turn of the screw. Also it possible to adjust with the knurled nut on an Aloris type tool post. Only thing is it gets heavy quick. The holder shown is the number 4 size knock off, better known as an Aloris CA holder.

Richard W.
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Steffin T
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Re: Large Concave Radius

Post by Steffin T » Sat Aug 06, 2011 5:31 pm

...Man... I "need" more tooling!

Thank you for the pics Richard, very nice. I may end up going that route rather than the bedair style. Took the compound slide off of the Clausing 5914 and noticed there is a "locating stud" beneath it, going up into the slide. It appears that it unscrews (looking at the manual) but am not sure how difficult that would be... will need to look further into it. If the stud proves too problematic, it would not be worth the effort in a bedair style since I would need to clear over an inch for the stud. After having to clearance the .50" for the tool slide, I think my height would be too much... Plus, it would be nice to not have to disassemble too much of the lathe just to use it.

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