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Dickson parting blade holder problem

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Scottmk110/06/2014 15:39:04
25 forum posts

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

Martin Kyte10/06/2014 16:21:24
avatar
2067 forum posts
37 photos

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

Jon Gibbs10/06/2014 16:23:27
739 forum posts

Hi Scott,

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

**LINK**

HTH

Jon

Martin Kyte10/06/2014 16:27:16
avatar
2067 forum posts
37 photos

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

Acrosticus10/06/2014 16:42:11
24 forum posts
2 photos

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

Scottmk110/06/2014 16:52:07
25 forum posts

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

Clive Foster10/06/2014 17:26:51
2386 forum posts
77 photos

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

JohnF10/06/2014 17:37:26
avatar
1024 forum posts
143 photos

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

Scottmk110/06/2014 17:46:28
25 forum posts

Hi John, can you suggest a supplier for the eclipse blades?

Scott

Clive Foster10/06/2014 19:07:05
2386 forum posts
77 photos

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.

end view.jpg

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

side view.jpg

Hope this helps.

Clive

Edited By Clive Foster on 10/06/2014 19:08:01

Scottmk110/06/2014 20:25:30
25 forum posts

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

JohnF10/06/2014 21:42:41
avatar
1024 forum posts
143 photos

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

WALLACE10/06/2014 21:54:37
304 forum posts
17 photos
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.
Scottmk110/06/2014 22:06:22
25 forum posts

I think due the parting blade being a trapezium section it wouldnt work very well upside down.

Scottmk110/06/2014 22:07:03
25 forum posts

Thanks for the link John, I will add it to my bookmarks for future reference.

Scott

Clive Foster10/06/2014 22:19:10
2386 forum posts
77 photos

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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