Dickson parting blade holder problem

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Dickson parting blade holder problem

This topic has 16 replies, 7 voices, and was last updated 10 June 2014 at 22:19 by Clive Foster.

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10 June 2014 at 15:39 #17410
Scottmk1
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@scottmk1
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10 June 2014 at 15:39 #154936
Scottmk1
Participant
@scottmk1
HI, I have a Boxford lathe with a T0 size Dickson tool holder set up. When I put a blade in the part off tool holder the blade tips over at the top. I'm thinking I may need the correct type of part off blade as the one I have at the minute is rectangular in section?

Here is a pic, excuse the quality of the photo but I think you can see the problem. Any advice appreciated.

Scott

Edited By Scottmk1 on 10/06/2014 15:41:08
10 June 2014 at 16:21 #154939
Martin Kyte
Participant
@martinkyte99762
Hi Scott, you could be right about the cross section but just a thought. You haven't just got a holder for a rear tool post with the blade upside down have you? Cant remember off hand what mine looks like.

regards Martin
10 June 2014 at 16:23 #154940
Jon Gibbs
Participant
@jongibbs59756
Hi Scott,

You could try to make an adaptor similar to the one I ended up with here…

**LINK**

HTH

Jon
10 June 2014 at 16:27 #154941
Martin Kyte
Participant
@martinkyte99762
Forget my suggestion just now. Had a look at the Myford page and the wedging strip is on the bottom for rear tool post. I do remember that my parting blades are wedge shaped in profile though.

Martin
10 June 2014 at 16:42 #154942
Acrosticus
Participant
@acrosticus
Hello Scott,

I think you need a blade with a trapezium X-section, i.e. an opposite bevel along both edges.

The 1/2" blade in my Myford-Dickson holder has the bevel edges: the holder is made for that type, presumably the same though might be a different height blade

Parting blades with right angled edges are rare in my experience: However the tiny 5/16" blade in my special Dickson rear tool post holder is T-shaped with a very narrow top to the tee, to give side clearance when cutting, and has no bevels. (Blades of this type are very difficult to find)

regards

Tony
10 June 2014 at 16:52 #154943
Scottmk1
Participant
@scottmk1
Thanks for the replies folks, very helpful. Tony, I think you are correct that I need a trapezium section parting blade, do you know where these can be sourced from?

Scott
10 June 2014 at 17:26 #154945
Clive Foster
Participant
@clivefoster55965
Both holder and blade have been bodged to make incorrect components go together.

The clamping wedge should be essentially symmetrical in shape and of a size such that when fully tightened with no blade inserted so the back of wedge and slot are in contact the lower wedge angle should almost contact the bottom corner of the slot. Clerance is thou's. Just enough to be sure there is no contact there when attempting to clamp the blade. The screw holes are a little above centre line. As I found out when making a stepped wedge to let my T2 size take next size down blades to use up my stash.

Blade should be narrower at bottom than top. Bottom edge should sit neatly in the toolpost groove, top edge angle should match the wedge angle. Top is fairly rough ground. presumably to ensure that folks aren't tempted to use the blade as is instead of grinding top flat on the projecting portion. For proper clearance in the cut slot when parting off the top must be ground back at leas as far as the maximum extension you plan use. I've never seen any need to angle the top or apply backrake. Continous coolant / lubrication whether by flood or mist seems best answer to parting problems.

With the correct size blade fitted the back of the clamping wedge should be very close to the back of the slot.

Mine have a second tapped hole in the base for the height setting collar stud to permit inverted use in a back tool post or with a reverse running (as per Britan) lathe.

Clive

Edited By Clive Foster on 10/06/2014 17:29:09
10 June 2014 at 17:37 #154947
JohnF
Participant
@johnf59703
Hi Scot, It will pay dividends in the long term to buy a genuine Eclipse blade, Dickson tool holders were designed for these. Yes they are expensive compared to the clones but they do WORK and that's what matters. I have tried the clones and frankly they are hopeless by comparison.

Moral don't economise on tooling you will pay more if you do.

regards John
10 June 2014 at 17:46 #154948
Scottmk1
Participant
@scottmk1
Hi John, can you suggest a supplier for the eclipse blades?

Scott
10 June 2014 at 19:07 #154958
Clive Foster
Participant
@clivefoster55965
Hi Scott

Couple of pictures of T2 size parting blade holders which may help.

First one shows end views of how the clamp works. One on left shows how smaller than standard blades can be fitted by making a stepped clamp. One on right is standard but no blade fitted 'cos I've run out of standard size ones.

Blade side view of same pair, should have used flash for picture but its just about OK.

Hope this helps.

Clive

Edited By Clive Foster on 10/06/2014 19:08:01
10 June 2014 at 20:25 #154972
Scottmk1
Participant
@scottmk1
Thanks for the pictures clive, as they say a picture says a thousand words. I have found a supplier on ebay for the eclipse blades in the correct size so I will purchase one of those.

Scott
10 June 2014 at 21:42 #154982
JohnF
Participant
@johnf59703
Hi Scot, MSC Supplies do them but I see you are fixed up from eBay , anyway here is the link

http://www.mscdirect.co.uk/ECB-61260E/SEARCH:CATEGORY/product.html

John
10 June 2014 at 21:54 #154983
WALLACE
Participant
@wallace
Possibly this should be in a new thread. .. but…

I have one one of these tool posts on my Harrison and it’s sometimes occurred to me to invert the holder to hopefully give the advantages in geometry in the same way as a rear mounted one. I have LOO taper so running the lathe in reverse won’t unscrew the chuck.

But the tool holder looks awfully hard – possibly too hard to drill and tap a hole to take a new ‘height adjusting stud’ that will be need.

Any thoughts if it’s ‘do-able’ ?

Thanks

W.
10 June 2014 at 22:06 #154987
Scottmk1
Participant
@scottmk1
I think due the parting blade being a trapezium section it wouldnt work very well upside down.
10 June 2014 at 22:07 #154988
Scottmk1
Participant
@scottmk1
Thanks for the link John, I will add it to my bookmarks for future reference.

Scott
10 June 2014 at 22:19 #154989
Clive Foster
Participant
@clivefoster55965
Wallace

As I mentioned above my holders already have threaded hole in the base so they can be set-up for inverted use. Be worth checking yours. It took me over a decade to notice!

Dickson holders are are hard, very hard. Drilling and tapping is quite impractical in the home shop.

A tool holding bolt thread in one of mine was damaged at the bottom (how?). After cursing and sweating the bolt out I attempted to clean it out using a nice new tap with brain temperature still too close to red mist mode for coherent reflection. It seemed to be working, albeit with some squealing but pushing a bit too far broke the tap. Which was even harder to get out. Eventual fix was to use use a "ball on a stick" grinding point out of my Lidl Dremel knock off tool and accessory kit to take out bottom thread.

Also had to take a 2 mm (ish) off the bottom of one holder so I could get a carbide tip parting blade down to centre height without fouling the upper surface of the topslide. The hand held angle grinder I used for the roughing out struggled to shift the material. Did it in the end but the spark shower was very anaemic. Similarly for the linisher when doing first cleans up despite a new abrasive band. Glad I had diamond files to finally finish off. Even they weren't over impressed.

Clive

Edited By Clive Foster on 10/06/2014 22:21:04
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