Cutting a dovetail

[sean logieParticipant @seanlogie69385]

Looking for some advice for using a dovetail cutter on a 250-101 tool holder I'm going to make out of steel stock . I will be using a 20mm hss cutter . Are the run speeds the same as a end mill of the same size .

Sean

[sean logieParticipant @seanlogie69385]

[richardandtracyParticipant @richardandtracy]

Planning on doing exactly the same thing myself, but in an aluminium block. The only difference is that our machinist at work suggested angling the block at 30° and machining the dovetail with a slot mill. If the back face of the dovetail groove is not flat, what of it? Makes sense, but until I've tried it on a practice piece I'm a bit nervous of the idea. Apparently he did it for home use with his 250-201 toolholders.

Mt first guess would be to treat as an HSS mill of the same diameter of the largest part.

I await answers with anticipation too.

Regards

Richard.

[Martin DowingParticipant @martindowing58466]

Read Harold Hall's milling tutorials for good idea how to do it.

In general make first square slot, then finish it off with dovetail cutter in few passes from each side. Make both sides in one setting to ensure good degree of parallelity, which is usually not too critical anyway as a gib strip will take care of it.

If it need to work really smooth, you will need to scrap it at the end and that is not easy.

Martin

[sean logieParticipant @seanlogie69385]

Thanks guys, I’ve already mill the square out ready for cutting the dovetail. My home made vertical head is not really suited to running fast enough for a small slot endmill .

Sean

[sean logieParticipant @seanlogie69385]

Posted by Martin Dowing on 22/04/2018 19:02:41:

Read Harold Hall's milling tutorials for good idea how to do it.

In general make first square slot, then finish it off with dovetail cutter in few passes from each side. Make both sides in one setting to ensure good degree of parallelity, which is usually not too critical anyway as a gib strip will take care of it.

If it need to work really smooth, you will need to scrap it at the end and that is not easy.

Martin

Hi Martin,there's not gib strip on the tool holder ,it's just a straight dovetail .

[JonParticipant @jon]

Sean i have machined many 250/200 series using quality as in expensive carbide cutters at £30+ a pop ie Seco and the like. Most will only last 3 to 5 opening up of the slots for the tools. Cheaper end of the carbide wont even do one pass and HSS are much less resilient to wear.

Cleanup i would risk it anything other than that gonna need dozens of dovetail cutters to do a couple, the tool holders are hard ish. First thing to go will be the edges, if finish with it will leave a roundover.

Ideally want interchangeable tipped dovetail cutter all the rage 20 yrs ago now no one does them, hence why i havent made any even in mild steel been lying there 2 yrs.

[JonParticipant @jon]

Just had a look though the 250/200 series are very similar in size to the 100 series the dovetails are fractionally smaller.

250/200 are 10.37mm deep dovetail. The HSS 60 degree dovetail cutters are only 7.8mm deep!
Still doable but will need to raise the cutter and blend in. Not ideal makes it a pain to get right where minimal play is required.

Theres a few online dovetail calculators one i dont recommend and may come up first in google. If stuck send me the dimensions using roll pins and i will put it through a purchased calculator.
Failing that could do it the trial and error way continually trying and sizing to match.

[Bill PudneyParticipant @billpudney37759]

If you have CAD, draw the dovetail, both male and female, pick a size of pin, preferably two that you have. Add the pins to the drawing, dimension the distance between the pins. Cut the dovetail. Easy peasy. I recently made 10 new holders for an OXA, 9 of them were perfect, one was a bit big so I glued in a piece of 0.004" shim, and bingo!!

cheers

Bill

[Bruce EdneyParticipant @bruceedney59949]

I have made a few 201-101 holders using a 20mm HSS cutter – 0.5mm doc after cutting the main slot out to about 36mm x 10.35mm deep and all went well – RPM was about the same as a 20mm HSS endmill but I get listened to the cutter and fed it in lightly. The cutter is still fine and hopefully should contiue to be so for some time.

Cheers

Bruce

[sean logieParticipant @seanlogie69385]

Thanks for all the advice ,have ordered a 20mm dovetail cutter .

Sean

[David ColwillParticipant @davidcolwill19261]

I did 15 of them not long ago with a HSS cutter that I had lying around. I ran mine slightly slower than I would for an endmill of the same size and used plenty of coolant. Be careful when breaking out of the cut as this is where there is a greater risk of losing a tooth.

I find that listening to how it sounds is as good a guide as anything.

My dovetail cutter lived to tell the tale and is ready for the next batch

Regards.

David.

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