Thread: Your latest project

Originally Posted by Oldneweng

At the bottom edge a relief of only 7.86 degrees is required.

Dean

I think I could achieve that by putting some shims between the mill table and the back end of the block that holds the chuck. This would disturb the other tool angles only slightly.

Just had a revelation, goes like this ......... inserts are designed so that when they are screwed onto a toolholder in the designed orientation, then the rake and the clearance are both working as designed. When people start using these bits "out of context" the rake and clearance can be changed significantly and the tool won't work as well as it might.

So its not just a matter of grabbing any old carbide bit and whacking it on a holder so that it cuts a 60 degree dovetail.

In my simple view of the world that was all I had to do. So am off to learn all I can about carbide bits now.

Now that I think about it, I have seen bits and toolholders that were specifically designed to cut dovetails, probably thought they were too expensive. The holders will be designed to present the bit to the work with proper rake and clearance and leave a 60 degree cut behind. This is discussed in one of those threads I posted above but I didnt understand it when I read it last night. Its just crystalised.

Bill

Last night I just quickly did a drawing. Today I completed aspects of the drawing.

Dovetail Cutter Geometry 2.jpg

Showing the full insert with an angled pocket shows that only an angle of 8.93 degrees will clear the edge at the top point. Is is evident tho that this puts the insert in a negative rake angle which is not ideal.

Changing the angle of the chuck axis when cutting the pocket will change the cutting angle. It will no longer cut at 60 degrees. This may not be a big issue if you are only using this for roughing tho.

I would be looking for a positive rake insert of a thinner cross section. Both of these will minimise the issue. The 14.97 angle I quoted in my previous post is the maximum angle affecting the cutting and is only relevant at the very top point of the insert which is actually non existent due to the radius of the insert tip. This angle will reduce down the flank as the cutting depth gets shallower. It will always be there tho if you use the tool later at a deeper depth.

I would like to make one of these cutters, but I have not been able to source suitable inserts.

Dean

I am not sure what you size restraints are, but I have drawn the cutter using a 50mm diam to see how it would work.

Dovetail Cutter Geometry 3.jpg

This is using a TCMT 16 insert 4mm thick. These inserts are the most common available, I would have some myself I think and they have a 7 deg relief angle.

The green line in the drawing shows this 7 degree angle. The 6.8 degrees shown is the angle between this green line and the tangent. There is 0.2 degrees clearance based on this drawing. This is the point I mention that I am not an expert and I may have missed something. I am only looking at 2 dimentional geometry.

Dean

Dean,

Look at how this cheeky lot copied my initial attempt and found the right cutters to make it work and put up a web page in just a few hours ..... efficiency plus.

1/2" Indexable 60 Dovetail Cutter - Dovetail Cutters - Indexable Cutting - Products

The cutters they use are here

TDEX21.51E Carbide Insert

Cannot find a supplier on ebay.

Although if you just google TDEX insert you do get a few hits but postage from USA.

This bloke on MEW in UK has done a terrific job using TCMT inserts

Dovetail cutter. | Model Engineer


Bill

Would you need to have a rigid mill in order to get the most out of a dovetail cutter ? Or use sharp inserts ?

Yeah Bill. I always maintain you can't trust anybody.

The problem I always came up against was the lack of suitable inserts. TDEX inserts are the elusive 15 degree relief ones. I don't know what the X is tho. My chart (Carbide Depot) does not list it.

Mike, I would say you would need a fairly rigid mill or cut the dovetails carefully. Either way you look at it you are cutting the full face width at the end of the cut. I have never cut one myself to be honest. It is something that would be useful to be able to do. When I have time to do projects like this that is. I cannot see myself having any spare time for some months now. Sigh.

Dean

Originally Posted by morrisman

Would you need to have a rigid mill in order to get the most out of a dovetail cutter ? Or use sharp inserts ?

My little RF30 seems to manage but as its the only mill I have ever used I cant really comment further.

With respect to the X in the insert name I think it means the insert is propriety ie owned and sold by only one company and isnt generally available on ebay like tcmt or tpgb or ccmt. Got that snippet on another forum.




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I have got my optical comparator pretty much operational again, while it cost me quite a few $ in stuff ups at the end of the day I could have got it fixed for $30 or so had I been more knowledgable in LED technology. Original bulbs for the profile part are rare and very pricey, the bulbs for the surface projection (1000W projector bulbs) are common and cheap ($10)


Some may have seen in the 3D printing thread how I 3D printed a LED holder. I actually made three versions, and the Mk3 version is the final one. Quite impressed with 3D printing and how easy it is to prototype.

I still have some tidying up to do and install a new 24V DC power supply for the LED but it is usable now. The LED is a 6500k high CRI Cree XHP35 outputting about 13W.

The entire lamphouse lens system has been replaced with a single aspherical lens, a massive $5 delivered from deal extreme. I printed out the holder for it only as I did not have any plastic rod near the right diameter. Aspherical lenses are apparently good with LED's to remove aberrations. In any case it works.

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Do you use it like a gigantic magnifying glass to look at tiny things in detail ?

Bill

It is essentially an inspection device. You measure features with it. From what I understand the machines are calibrated so say your magnification is 10X, what shows on the screen is exactly 10X and the screen itself has all sorts of direct measuring markings on it like for radius and length measurement. Mine only has crosshairs. The better ones also have a rotating screen with angle measurement.

In this day and age you can also print out transparencies on a printer and put that on the screen to use as your template.

The part sits on a table that moves left right and up down (and in out for focus for this model) You can fit scales to the movement and measure features that way (how I do it).

Also my machine has surface illumination, that directs a large light source (the 1000W bulb) through the machine to bounce off the surface of the workpiece and back onto the screen. That is switched on in the picture of the thread gauge above. You can see a back to front 20? That is stamped into the part being reflected.

This model is made by Kodak and old, they came out around or just after WW2.

After using the two sets of Kant Twist clamps that I made previously for a couple of years, I found that a larger set would be useful. I wanted a set that could clamp onto a 150mm size object and have a deeper throat than the standard design. I checked out several different designs and made up a couple of paper models to make sure the thrust line of the screw thread maintained its alignment over the clamping range. The design I chose is very close to the original Kant Twist shape, this enables you to have a shorter threaded section with good alignment and was the most compact design. This set of clamps I made from 4mm steel plate and used 316 stainless steel all thread for the 12mm thread a for the clamp feet. The finished clamps open out to 175MM and have a throat depth of 135mm.
Bob

Today I made a small lpg burner out of scrap steel and an old oxy torch tip, I did a test run and was able to easily melt down some aluminium, I'll try it on some brass next
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The little furnace refractory material is a mix of perlite, aluminium oxide and sodium silicate.

I successfully melted down a small piece of brass this morning, almost had an accident when the steel tube I was using as a crucible stand off partially melted and collapsed.
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I think I'll try some small scale lost foam casting next and report back with the results.

Nice work Any chance of some details on how you made the burner, please?
What sort of brass did you use, old tap ware, or something else, look forward to seeing the results of the foam process??
Kryn

I made this for the milling table. Much faster to bring the table up and down with the cordless drill now.

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